The Emacs Editor

Emacs is the extensible, customizable, self-documenting real-time
display editor. This manual describes how to edit with Emacs and
some of the ways to customize it; it corresponds to GNU Emacs version
24.5.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being “The GNU Manifesto,” “Distribution” and
“GNU GENERAL PUBLIC LICENSE,” with the Front-Cover Texts being “A GNU
Manual,” and with the Back-Cover Texts as in (a) below. A copy of the
license is included in the section entitled “GNU Free Documentation
License.”

(a) The FSF’s Back-Cover Text is: “You have the freedom to copy and
modify this GNU manual. Buying copies from the FSF supports it in
developing GNU and promoting software freedom.”

Distribution

GNU Emacs is free software; this means that everyone is free to
use it and free to redistribute it under certain conditions. GNU Emacs
is not in the public domain; it is copyrighted and there are
restrictions on its distribution, but these restrictions are designed
to permit everything that a good cooperating citizen would want to do.
What is not allowed is to try to prevent others from further sharing
any version of GNU Emacs that they might get from you. The precise
conditions are found in the GNU General Public License that comes with
Emacs and also appears in this manual1.
See Copying.

One way to get a copy of GNU Emacs is from someone else who has it.
You need not ask for our permission to do so, or tell any one else;
just copy it. If you have access to the Internet, you can get the
latest distribution version of GNU Emacs by anonymous FTP; see
http://www.gnu.org/software/emacs on our website for more
information.

You may also receive GNU Emacs when you buy a computer. Computer
manufacturers are free to distribute copies on the same terms that apply to
everyone else. These terms require them to give you the full sources,
including whatever changes they may have made, and to permit you to
redistribute the GNU Emacs received from them under the usual terms of the
General Public License. In other words, the program must be free for you
when you get it, not just free for the manufacturer.

If you find GNU Emacs useful, please send a donation to the
Free Software Foundation to support our work. Donations to the Free
Software Foundation are tax deductible in the US. If you use GNU Emacs
at your workplace, please suggest that the company make a donation.
To donate, see https://my.fsf.org/donate/.
For other ways in which you can help, see
http://www.gnu.org/help/help.html.

We also sell hardcopy versions of this manual and An
Introduction to Programming in Emacs Lisp, by Robert J. Chassell.
You can visit our online store at http://shop.fsf.org/.
The income from sales goes to support the foundation’s purpose: the
development of new free software, and improvements to our existing
programs including GNU Emacs.

Introduction

You are reading about GNU Emacs, the GNU incarnation of the
advanced, self-documenting, customizable, extensible editor Emacs.
(The ‘G’ in
GNU (GNU’s Not Unix)
is not silent.)

We call Emacs advanced because it can do much more than simple
insertion and deletion of text. It can control subprocesses, indent
programs automatically, show multiple files at once, and more.
Emacs editing commands operate in terms of characters, words, lines,
sentences, paragraphs, and pages, as well as expressions and comments
in various programming languages.

Self-documenting means that at any time you can use special
commands, known as help commands, to find out what your options
are, or to find out what any command does, or to find all the
commands that pertain to a given topic. See Help.

Customizable means that you can easily alter the behavior of
Emacs commands in simple ways. For instance, if you use a programming
language in which comments start with ‘<**’ and end with
‘**>’, you can tell the Emacs comment manipulation commands to
use those strings (see Comments). To take another example, you
can rebind the basic cursor motion commands (up, down, left and right)
to any keys on the keyboard that you find comfortable.
See Customization.

Extensible means that you can go beyond simple customization
and create entirely new commands. New commands are simply programs
written in the Lisp language, which are run by Emacs’s own Lisp
interpreter. Existing commands can even be redefined in the middle of
an editing session, without having to restart Emacs. Most of the
editing commands in Emacs are written in Lisp; the few exceptions
could have been written in Lisp but use C instead for efficiency.
Writing an extension is programming, but non-programmers can use it
afterwards. See Preface in An
Introduction to Programming in Emacs Lisp, if you want to learn Emacs
Lisp programming.

1 The Organization of the Screen

On a graphical display, such as on GNU/Linux using the X Window
System, Emacs occupies a “graphical window”. On a text terminal,
Emacs occupies the entire terminal screen. We will use the term
frame to mean a graphical window or terminal screen occupied by
Emacs. Emacs behaves very similarly on both kinds of frames. It
normally starts out with just one frame, but you can create additional
frames if you wish (see Frames).

Each frame consists of several distinct regions. At the top of the
frame is a menu bar, which allows you to access commands via a
series of menus. On a graphical display, directly below the menu bar
is a tool bar, a row of icons that perform editing commands if
you click on them. At the very bottom of the frame is an echo
area, where informative messages are displayed and where you enter
information when Emacs asks for it.

The main area of the frame, below the tool bar (if one exists) and
above the echo area, is called the window. Henceforth in this
manual, we will use the word “window” in this sense. Graphical
display systems commonly use the word “window” with a different
meaning; but, as stated above, we refer to those “graphical windows”
as “frames”.

An Emacs window is where the buffer—the text you are
editing—is displayed. On a graphical display, the window possesses
a scroll bar on one side, which can be used to scroll through
the buffer. The last line of the window is a mode line. This
displays various information about what is going on in the buffer,
such as whether there are unsaved changes, the editing modes that are
in use, the current line number, and so forth.

When you start Emacs, there is normally only one window in the
frame. However, you can subdivide this window horizontally or
vertically to create multiple windows, each of which can independently
display a buffer (see Windows).

At any time, one window is the selected window. On a
graphical display, the selected window shows a more prominent cursor
(usually solid and blinking); other windows show a less prominent
cursor (usually a hollow box). On a text terminal, there is only one
cursor, which is shown in the selected window. The buffer displayed
in the selected window is called the current buffer, and it is
where editing happens. Most Emacs commands implicitly apply to the
current buffer; the text displayed in unselected windows is mostly
visible for reference. If you use multiple frames on a graphical
display, selecting a particular frame selects a window in that frame.

1.1 Point

The cursor in the selected window shows the location where most
editing commands take effect, which is called point2. Many Emacs commands move point
to different places in the buffer; for example, you can place point by
clicking mouse button 1 (normally the left button) at the desired
location.

By default, the cursor in the selected window is drawn as a solid
block and appears to be on a character, but you should think of
point as between two characters; it is situated before
the character under the cursor. For example, if your text looks like
‘frob’ with the cursor over the ‘b’, then point is between
the ‘o’ and the ‘b’. If you insert the character ‘!’
at that position, the result is ‘fro!b’, with point between the
‘!’ and the ‘b’. Thus, the cursor remains over the
‘b’, as before.

If you are editing several files in Emacs, each in its own buffer,
each buffer has its own value of point. A buffer that is not
currently displayed remembers its value of point if you later display
it again. Furthermore, if a buffer is displayed in multiple windows,
each of those windows has its own value of point.

See Cursor Display, for options that control how Emacs displays
the cursor.

1.2 The Echo Area

The line at the very bottom of the frame is the echo area. It
is used to display small amounts of text for various purposes.

The echo area is so-named because one of the things it is used for
is echoing, which means displaying the characters of a
multi-character command as you type. Single-character commands are
not echoed. Multi-character commands (see Keys) are echoed if you
pause for more than a second in the middle of a command. Emacs then
echoes all the characters of the command so far, to prompt you for the
rest. Once echoing has started, the rest of the command echoes
immediately as you type it. This behavior is designed to give
confident users fast response, while giving hesitant users maximum
feedback.

The echo area is also used to display an error message when a
command cannot do its job. Error messages may be accompanied by
beeping or by flashing the screen.

Some commands display informative messages in the echo area to tell
you what the command has done, or to provide you with some specific
information. These informative messages, unlike error messages,
are not accompanied with a beep or flash. For example, C-x =
(hold down Ctrl and type x, then let go of Ctrl and
type =) displays a message describing the character at point,
its position in the buffer, and its current column in the window.
Commands that take a long time often display messages ending in
‘...’ while they are working (sometimes also indicating how much
progress has been made, as a percentage), and add ‘done’ when
they are finished.

Informative echo area messages are saved in a special buffer named
*Messages*. (We have not explained buffers yet; see
Buffers, for more information about them.) If you miss a
message that appeared briefly on the screen, you can switch to the
*Messages* buffer to see it again. The *Messages*
buffer is limited to a certain number of lines, specified by the
variable message-log-max. (We have not explained variables
either; see Variables, for more information about them.) Beyond
this limit, one line is deleted from the beginning whenever a new
message line is added at the end.

See Display Custom, for options that control how Emacs uses the
echo area.

The echo area is also used to display the minibuffer, a
special window where you can input arguments to commands, such as the
name of a file to be edited. When the minibuffer is in use, the text
displayed in the echo area begins with a prompt string, and the
active cursor appears within the minibuffer, which is temporarily
considered the selected window. You can always get out of the
minibuffer by typing C-g. See Minibuffer.

1.3 The Mode Line

At the bottom of each window is a mode line, which describes
what is going on in the current buffer. When there is only one
window, the mode line appears right above the echo area; it is the
next-to-last line in the frame. On a graphical display, the mode line
is drawn with a 3D box appearance. Emacs also usually draws the mode
line of the selected window with a different color than that of
unselected windows, in order to make it stand out.

The text displayed in the mode line has the following format:

cs:ch-frbufposline (majorminor)

On a text terminal, this text is followed by a series of dashes
extending to the right edge of the window. These dashes are omitted
on a graphical display.

The cs string and the colon character after it describe the
character set and newline convention used for the current buffer.
Normally, Emacs automatically handles these settings for you, but it
is sometimes useful to have this information.

cs describes the character set of the text in the buffer
(see Coding Systems). If it is a dash (‘-’), that indicates
no special character set handling (with the possible exception of
end-of-line conventions, described in the next paragraph). ‘=’
means no conversion whatsoever, and is usually used for files
containing non-textual data. Other characters represent various
coding systems—for example, ‘1’ represents ISO Latin-1.

On a text terminal, cs is preceded by two additional
characters that describe the coding systems for keyboard input and
terminal output. Furthermore, if you are using an input method,
cs is preceded by a string that identifies the input method
(see Input Methods).

The character after cs is usually a colon. If a different
string is displayed, that indicates a nontrivial end-of-line
convention for encoding a file. Usually, lines of text are separated
by newline characters in a file, but two other conventions are
sometimes used. The MS-DOS convention uses a “carriage-return”
character followed by a “linefeed” character; when editing such
files, the colon changes to either a backslash (‘\’) or
‘(DOS)’, depending on the operating system. Another convention,
employed by older Macintosh systems, uses a “carriage-return”
character instead of a newline; when editing such files, the colon
changes to either a forward slash (‘/’) or ‘(Mac)’. On some
systems, Emacs displays ‘(Unix)’ instead of the colon for files
that use newline as the line separator.

The next element on the mode line is the string indicated by
ch. This shows two dashes (‘--’) if the buffer displayed
in the window has the same contents as the corresponding file on the
disk; i.e., if the buffer is “unmodified”. If the buffer is
modified, it shows two stars (‘**’). For a read-only buffer, it
shows ‘%*’ if the buffer is modified, and ‘%%’ otherwise.

The character after ch is normally a dash (‘-’).
However, if the default-directory for the current buffer is on a
remote machine, ‘@’ is displayed instead (see File Names).

fr gives the selected frame name (see Frames). It appears
only on text terminals. The initial frame’s name is ‘F1’.

buf is the name of the buffer displayed in the window.
Usually, this is the same as the name of a file you are editing.
See Buffers.

pos tells you whether there is additional text above the top
of the window, or below the bottom. If your buffer is small and all
of it is visible in the window, pos is ‘All’. Otherwise,
it is ‘Top’ if you are looking at the beginning of the buffer,
‘Bot’ if you are looking at the end of the buffer, or
‘nn%’, where nn is the percentage of the buffer above
the top of the window. With Size Indication mode, you can display the
size of the buffer as well. See Optional Mode Line.

line is the character ‘L’ followed by the line number at
point. (You can display the current column number too, by turning on
Column Number mode. See Optional Mode Line.)

major is the name of the major mode used in the buffer.
A major mode is a principal editing mode for the buffer, such as Text
mode, Lisp mode, C mode, and so forth. See Major Modes. Some
major modes display additional information after the major mode name.
For example, Compilation buffers and Shell buffers display the status
of the subprocess.

minor is a list of some of the enabled minor modes,
which are optional editing modes that provide additional features on
top of the major mode. See Minor Modes.

Some features are listed together with the minor modes whenever they
are turned on, even though they are not really minor modes.
‘Narrow’ means that the buffer being displayed has editing
restricted to only a portion of its text (see Narrowing).
‘Def’ means that a keyboard macro is currently being defined
(see Keyboard Macros).

In addition, if Emacs is inside a recursive editing level, square
brackets (‘[…]’) appear around the parentheses that
surround the modes. If Emacs is in one recursive editing level within
another, double square brackets appear, and so on. Since recursive
editing levels affect Emacs globally, such square brackets appear in
the mode line of every window. See Recursive Edit.

You can change the appearance of the mode line as well as the format
of its contents. See Optional Mode Line. In addition, the mode
line is mouse-sensitive; clicking on different parts of the mode line
performs various commands. See Mode Line Mouse.

1.4 The Menu Bar

Each Emacs frame normally has a menu bar at the top which you
can use to perform common operations. There’s no need to list them
here, as you can more easily see them yourself.

On a display that supports a mouse, you can use the mouse to choose a
command from the menu bar. An arrow on the right edge of a menu item
means it leads to a subsidiary menu, or submenu. A ‘...’
at the end of a menu item means that the command will prompt you for
further input before it actually does anything.

Some of the commands in the menu bar have ordinary key bindings as
well; if so, a key binding is shown in parentheses after the item
itself. To view the full command name and documentation for a menu
item, type C-h k, and then select the menu bar with the mouse in
the usual way (see Key Help).

Instead of using the mouse, you can also invoke the first menu bar
item by pressing F10 (to run the command menu-bar-open).
You can then navigate the menus with the arrow keys. To activate a
selected menu item, press RET; to cancel menu navigation, press
C-g or ESCESCESC.

On a text terminal, you can optionally access the menu-bar menus in
the echo area. To this end, customize the variable
tty-menu-open-use-tmm to a non-nil value. Then typing
F10 will run the command tmm-menubar instead of dropping
down the menu. (You can also type M-`, which always invokes
tmm-menubar.) tmm-menubar lets you select a menu item
with the keyboard. A provisional choice appears in the echo area.
You can use the up and down arrow keys to move through the menu to
different items, and then you can type RET to select the item.
Each menu item is also designated by a letter or digit (usually the
initial of some word in the item’s name). This letter or digit is
separated from the item name by ‘==>’. You can type the item’s
letter or digit to select the item.

2 Kinds of User Input

GNU Emacs is primarily designed for use with the keyboard. While it
is possible to use the mouse to issue editing commands through the
menu bar and tool bar, that is not as efficient as using the keyboard.
Therefore, this manual mainly documents how to edit with the keyboard.

Keyboard input into Emacs is based on a heavily-extended version of
ASCII. Simple characters, like ‘a’, ‘B’,
‘3’, ‘=’, and the space character (denoted as SPC),
are entered by typing the corresponding key. Control
characters, such as RET, TAB, DEL, ESC,
F1, Home, and LEFT, are also entered this way, as
are certain characters found on non-English keyboards
(see International).

Emacs also recognizes control characters that are entered using
modifier keys. Two commonly-used modifier keys are
Control (usually labeled Ctrl), and META (usually
labeled Alt)3. For example, Control-a is entered by
holding down the Ctrl key while pressing a; we will refer
to this as C-a for short. Similarly META-a, or M-a
for short, is entered by holding down the Alt key and pressing
a. Modifier keys can also be applied to non-alphanumerical
characters, e.g., C-F1 or M-LEFT.

You can also type Meta characters using two-character sequences
starting with ESC. Thus, you can enter M-a by typing
ESC a. You can enter C-M-a by typing ESC
C-a. Unlike META, ESC is entered as a separate
character. You don’t hold down ESC while typing the next
character; instead, press ESC and release it, then enter the
next character. This feature is useful on certain text terminals
where the META key does not function reliably.

On graphical displays, the window manager might block some keyboard
inputs, including M-TAB, M-SPC, C-M-d
and C-M-l. If you have this problem, you can either customize
your window manager to not block those keys, or “rebind” the
affected Emacs commands (see Customization).

Simple characters and control characters, as well as certain
non-keyboard inputs such as mouse clicks, are collectively referred to
as input events. For details about how Emacs internally handles
input events, see Input Events in The Emacs Lisp Reference
Manual.

3 Keys

Some Emacs commands are invoked by just one input event; for
example, C-f moves forward one character in the buffer. Other
commands take two or more input events to invoke, such as C-x
C-f and C-x 4 C-f.

A key sequence, or key for short, is a sequence of one
or more input events that is meaningful as a unit. If a key sequence
invokes a command, we call it a complete key; for example,
C-f, C-x C-f and C-x 4 C-f are all complete keys.
If a key sequence isn’t long enough to invoke a command, we call it a
prefix key; from the preceding example, we see that C-x
and C-x 4 are prefix keys. Every key sequence is either a
complete key or a prefix key.

A prefix key combines with the following input event to make a
longer key sequence. For example, C-x is a prefix key, so
typing C-x alone does not invoke a command; instead, Emacs waits
for further input (if you pause for longer than a second, it echoes
the C-x key to prompt for that input; see Echo Area).
C-x combines with the next input event to make a two-event key
sequence, which could itself be a prefix key (such as C-x 4), or
a complete key (such as C-x C-f). There is no limit to the
length of key sequences, but in practice they are seldom longer than
three or four input events.

You can’t add input events onto a complete key. For example,
because C-f is a complete key, the two-event sequence C-f
C-k is two key sequences, not one.

By default, the prefix keys in Emacs are C-c, C-h,
C-x, C-x RET, C-x @, C-x a, C-x
n, C-x r, C-x v, C-x 4, C-x 5, C-x 6,
ESC, M-g, and M-o. (F1 and F2 are
aliases for C-h and C-x 6.) This list is not cast in
stone; if you customize Emacs, you can make new prefix keys. You
could even eliminate some of the standard ones, though this is not
recommended for most users; for example, if you remove the prefix
definition of C-x 4, then C-x 4 C-f becomes an invalid key
sequence. See Key Bindings.

Typing the help character (C-h or F1) after a prefix key
displays a list of the commands starting with that prefix. The sole
exception to this rule is ESC: ESC C-h is equivalent
to C-M-h, which does something else entirely. You can, however,
use F1 to display a list of commands starting with ESC.

4 Keys and Commands

This manual is full of passages that tell you what particular keys
do. But Emacs does not assign meanings to keys directly. Instead,
Emacs assigns meanings to named commands, and then gives keys
their meanings by binding them to commands.

Every command has a name chosen by a programmer. The name is
usually made of a few English words separated by dashes; for example,
next-line or forward-word. Internally, each command is
a special type of Lisp function, and the actions associated with
the command are performed by running the function. See What Is a Function in The Emacs Lisp Reference
Manual.

The bindings between keys and commands are recorded in tables called
keymaps. See Keymaps.

When we say that “C-n moves down vertically one line” we are
glossing over a subtle distinction that is irrelevant in ordinary use,
but vital for Emacs customization. The command next-line does
a vertical move downward. C-n has this effect because it
is bound to next-line. If you rebind C-n to the command
forward-word, C-n will move forward one word instead.

In this manual, we will often speak of keys like C-n as
commands, even though strictly speaking the key is bound to a command.
Usually we state the name of the command which really does the work in
parentheses after mentioning the key that runs it. For example, we
will say that “The command C-n (next-line) moves point
vertically down”, meaning that the command next-line moves
vertically down, and the key C-n is normally bound to it.

Since we are discussing customization, we should tell you about
variables. Often the description of a command will say, “To
change this, set the variable mumble-foo.” A variable is a
name used to store a value. Most of the variables documented in this
manual are meant for customization: some command or other part of
Emacs examines the variable and behaves differently according to the
value that you set. You can ignore the information about variables
until you are interested in customizing them. Then read the basic
information on variables (see Variables) and the information about
specific variables will make sense.

5 Entering Emacs

The usual way to invoke Emacs is with the shell command
emacs. From a terminal window running in the X Window
System, you can run Emacs in the background with emacs &;
this way, Emacs won’t tie up the terminal window, so you can use it to
run other shell commands.

When Emacs starts up, the initial frame displays a special buffer
named ‘*GNU Emacs*’. This startup screen contains
information about Emacs and links to common tasks that are
useful for beginning users. For instance, activating the ‘Emacs
Tutorial’ link opens the Emacs tutorial; this does the same thing as
the command C-h t (help-with-tutorial). To activate a
link, either move point onto it and type RET, or click on
it with mouse-1 (the left mouse button).

Using a command line argument, you can tell Emacs to visit one or
more files as soon as it starts up. For example, emacs
foo.txt starts Emacs with a buffer displaying the contents of the
file ‘foo.txt’. This feature exists mainly for compatibility
with other editors, which are designed to be launched from the shell
for short editing sessions. If you call Emacs this way, the initial
frame is split into two windows—one showing the specified file, and
the other showing the startup screen. See Windows.

Generally, it is unnecessary and wasteful to start Emacs afresh each
time you want to edit a file. The recommended way to use Emacs is to
start it just once, just after you log in, and do all your editing in
the same Emacs session. See Files, for information on visiting
more than one file. If you use Emacs this way, the Emacs session
accumulates valuable context, such as the kill ring, registers, undo
history, and mark ring data, which together make editing more
convenient. These features are described later in the manual.

To edit a file from another program while Emacs is running, you can
use the emacsclient helper program to open a file in the
existing Emacs session. See Emacs Server.

Emacs accepts other command line arguments that tell it to load
certain Lisp files, where to put the initial frame, and so forth.
See Emacs Invocation.

If the variable inhibit-startup-screen is non-nil,
Emacs does not display the startup screen. In that case, if one or
more files were specified on the command line, Emacs simply displays
those files; otherwise, it displays a buffer named *scratch*,
which can be used to evaluate Emacs Lisp expressions interactively.
See Lisp Interaction. You can set the variable
inhibit-startup-screen using the Customize facility
(see Easy Customization), or by editing your initialization file
(see Init File).4

You can also force Emacs to display a file or directory at startup
by setting the variable initial-buffer-choice to a string
naming that file or directory. The value of
initial-buffer-choice may also be a function (of no arguments)
that should return a buffer which is then displayed.
If initial-buffer-choice is non-nil, then if you specify
any files on the command line, Emacs still visits them, but does not
display them initially.

6 Exiting Emacs

C-x C-c

Kill Emacs (save-buffers-kill-terminal).

C-z

On a text terminal, suspend Emacs; on a graphical display,
“minimize” the selected frame (suspend-emacs).

Killing Emacs means terminating the Emacs program. To do
this, type C-x C-c (save-buffers-kill-terminal). A
two-character key sequence is used to make it harder to type by
accident. If there are any modified file-visiting buffers when you
type C-x C-c, Emacs first offers to save these buffers. If you
do not save them all, it asks for confirmation again, since the
unsaved changes will be lost. Emacs also asks for confirmation if any
subprocesses are still running, since killing Emacs will also kill the
subprocesses (see Shell).

C-x C-c behaves specially if you are using Emacs as a server.
If you type it from a “client frame”, it closes the client
connection. See Emacs Server.

Emacs can, optionally, record certain session information when you
kill it, such as the files you were visiting at the time. This
information is then available the next time you start Emacs.
See Saving Emacs Sessions.

If the value of the variable confirm-kill-emacs is
non-nil, C-x C-c assumes that its value is a predicate
function, and calls that function. If the result of the function call
is non-nil, the session is killed, otherwise Emacs continues to
run. One convenient function to use as the value of
confirm-kill-emacs is the function yes-or-no-p. The
default value of confirm-kill-emacs is nil.

To kill Emacs without being prompted about saving, type M-x
kill-emacs.

C-z runs the command suspend-frame. On a graphical
display, this command minimizes (or iconifies) the
selected Emacs frame, hiding it in a way that lets you bring it back
later (exactly how this hiding occurs depends on the window system).
On a text terminal, the C-z command suspends Emacs,
stopping the program temporarily and returning control to the parent
process (usually a shell); in most shells, you can resume Emacs after
suspending it with the shell command %emacs.

Text terminals usually listen for certain special characters whose
meaning is to kill or suspend the program you are running. This
terminal feature is turned off while you are in Emacs. The meanings
of C-z and C-x C-c as keys in Emacs were inspired by the
use of C-z and C-c on several operating systems as the
characters for stopping or killing a program, but that is their only
relationship with the operating system. You can customize these keys
to run any commands of your choice (see Keymaps).

7 Basic Editing Commands

Here we explain the basics of how to enter text, make corrections,
and save the text in a file. If this material is new to you, we
suggest you first run the Emacs learn-by-doing tutorial, by typing
C-h t (help-with-tutorial).

7.1 Inserting Text

You can insert an ordinary graphic character (e.g., ‘a’,
‘B’, ‘3’, and ‘=’) by typing the associated key. This
adds the character to the buffer at point. Insertion moves point
forward, so that point remains just after the inserted text.
See Point.

To end a line and start a new one, type RET (newline).
(The RET key may be labeled Return or Enter on your
keyboard, but we refer to it as RET in this manual.) This
command inserts a newline character into the buffer, then indents
(see Indentation) according to the major mode. If point is at the end
of the line, the effect is to create a new blank line after it and
indent the new line; if point is in the middle of a line, the line is
split at that position. To turn off the auto-indentation, you can
either disable Electric Indent mode (see Indent Convenience) or
type C-j, which inserts just a newline, without any
auto-indentation.

As we explain later in this manual, you can change the way Emacs
handles text insertion by turning on minor modes. For instance,
the minor mode called Auto Fill mode splits lines automatically when
they get too long (see Filling). The minor mode called Overwrite
mode causes inserted characters to replace (overwrite) existing text,
instead of shoving it to the right. See Minor Modes.

Only graphic characters can be inserted by typing the associated
key; other keys act as editing commands and do not insert themselves.
For instance, DEL runs the command delete-backward-char
by default (some modes bind it to a different command); it does not
insert a literal ‘DEL’ character (ASCII character code
127).

To insert a non-graphic character, or a character that your keyboard
does not support, first quote it by typing C-q
(quoted-insert). There are two ways to use C-q:

C-q followed by any non-graphic character (even C-g)
inserts that character. For instance, C-q DEL inserts a
literal ‘DEL’ character.

C-q followed by a sequence of octal digits inserts the character
with the specified octal character code. You can use any number of
octal digits; any non-digit terminates the sequence. If the
terminating character is RET, that RET serves only to
terminate the sequence. Any other non-digit terminates the sequence
and then acts as normal input—thus, C-q 1 0 1 B inserts
‘AB’.

The use of octal sequences is disabled in ordinary non-binary
Overwrite mode, to give you a convenient way to insert a digit instead
of overwriting with it.

To use decimal or hexadecimal instead of octal, set the variable
read-quoted-char-radix to 10 or 16. If the radix is 16,
the letters a to f serve as part of a character code,
just like digits. Case is ignored.

Alternatively, you can use the command C-x 8 RET
(insert-char). This prompts for the Unicode name or code-point
of a character, using the minibuffer. If you enter a name, the
command provides completion (see Completion). If you enter a
code-point, it should be as a hexadecimal number (the convention for
Unicode), or a number with a specified radix, e.g., #o23072
(octal); See Integer Basics in The Emacs Lisp Reference
Manual. The command then inserts the corresponding character into
the buffer. For example, both of the following insert the infinity
sign (Unicode code-point U+221E):

C-x 8 RET infinity RETC-x 8 RET 221e RET

A numeric argument to C-q or C-x 8 RET specifies
how many copies of the character to insert (see Arguments).

7.2 Changing the Location of Point

To do more than insert characters, you have to know how to move
point (see Point). The keyboard commands C-f, C-b,
C-n, and C-p move point to the right, left, down, and up,
respectively. You can also move point using the arrow keys
present on most keyboards: RIGHT, LEFT,
DOWN, and UP; however, many Emacs users find
that it is slower to use the arrow keys than the control keys, because
you need to move your hand to the area of the keyboard where those
keys are located.

You can also click the left mouse button to move point to the
position clicked. Emacs also provides a variety of additional
keyboard commands that move point in more sophisticated ways.

C-f

Move forward one character (forward-char).

RIGHT

This command (right-char) behaves like C-f, with one
exception: when editing right-to-left scripts such as Arabic, it
instead moves backward if the current paragraph is a
right-to-left paragraph. See Bidirectional Editing. If
visual-order-cursor-movement is non-nil, this command
moves to the character that is to the right of the current screen
position, moving to the next or previous screen line as appropriate.
Note that this might potentially move point many buffer positions
away, depending on the surrounding bidirectional context.

C-b

Move backward one character (backward-char).

LEFT

This command (left-char) behaves like C-b, except it
moves forward if the current paragraph is right-to-left.
See Bidirectional Editing. If visual-order-cursor-movement
is non-nil, this command moves to the character that is to the
left of the current screen position, moving to the previous or next
screen line as appropriate.

C-n

DOWN

Move down one screen line (next-line). This command attempts
to keep the horizontal position unchanged, so if you start in the
middle of one line, you move to the middle of the next.

C-p

UP

Move up one screen line (previous-line). This command
preserves position within the line, like C-n.

C-a

Home

Move to the beginning of the line (move-beginning-of-line).

C-e

End

Move to the end of the line (move-end-of-line).

M-f

Move forward one word (forward-word).

C-RIGHT

M-RIGHT

This command (right-word) behaves like M-f, except it
moves backward by one word if the current paragraph is
right-to-left. See Bidirectional Editing.

M-b

Move backward one word (backward-word).

C-LEFT

M-LEFT

This command (left-word) behaves like M-b, except it
moves forward by one word if the current paragraph is
right-to-left. See Bidirectional Editing.

M-r

Without moving the text on the screen, reposition point on the left
margin of the center-most text line of the window; on subsequent
consecutive invocations, move point to the left margin of the top-most
line, the bottom-most line, and so forth, in cyclic order
(move-to-window-line-top-bottom).

A numeric argument says which screen line to place point on, counting
downward from the top of the window (zero means the top line). A
negative argument counts lines up from the bottom (-1 means the
bottom line). See Arguments, for more information on numeric
arguments.

M-<

Move to the top of the buffer (beginning-of-buffer). With
numeric argument n, move to n/10 of the way from the top.

M->

Move to the end of the buffer (end-of-buffer).

C-v

PageDown

next

Scroll the display one screen forward, and move point onscreen if
necessary (scroll-up-command). See Scrolling.

M-v

PageUp

prior

Scroll one screen backward, and move point onscreen if necessary
(scroll-down-command). See Scrolling.

M-g c

Read a number n and move point to buffer position n.
Position 1 is the beginning of the buffer.

M-g M-g

M-g g

Read a number n and move point to the beginning of line number
n (goto-line). Line 1 is the beginning of the buffer. If
point is on or just after a number in the buffer, that is the default
for n. Just type RET in the minibuffer to use it. You can
also specify n by giving M-g M-g a numeric prefix argument.
See Select Buffer, for the behavior of M-g M-g when you give it
a plain prefix argument.

M-g TAB

Read a number n and move to column n in the current line.
Column 0 is the leftmost column. If called with a prefix argument,
move to the column number specified by the argument’s numeric value.

C-x C-n

Use the current column of point as the semipermanent goal column
for C-n and C-p (set-goal-column). When a
semipermanent goal column is in effect, those commands always try to
move to this column, or as close as possible to it, after moving
vertically. The goal column remains in effect until canceled.

C-u C-x C-n

Cancel the goal column. Henceforth, C-n and C-p try to
preserve the horizontal position, as usual.

When a line of text in the buffer is longer than the width of the
window, Emacs usually displays it on two or more screen lines.
For convenience, C-n and C-p move point by screen lines,
as do the equivalent keys down and up. You
can force these commands to move according to logical lines
(i.e., according to the text lines in the buffer) by setting the
variable line-move-visual to nil; if a logical line
occupies multiple screen lines, the cursor then skips over the
additional screen lines. For details, see Continuation Lines.
See Variables, for how to set variables such as
line-move-visual.

Unlike C-n and C-p, most of the Emacs commands that work
on lines work on logical lines. For instance, C-a
(move-beginning-of-line) and C-e
(move-end-of-line) respectively move to the beginning and end
of the logical line. Whenever we encounter commands that work on
screen lines, such as C-n and C-p, we will point these
out.

When line-move-visual is nil, you can also set the
variable track-eol to a non-nil value. Then C-n
and C-p, when starting at the end of the logical line, move to
the end of the next logical line. Normally, track-eol is
nil.

C-n normally stops at the end of the buffer when you use it on
the last line in the buffer. However, if you set the variable
next-line-add-newlines to a non-nil value, C-n on
the last line of a buffer creates an additional line at the end and
moves down into it.

7.3 Erasing Text

Delete the character before point, or the region if it is active
(delete-backward-char).

Delete

Delete the character after point, or the region if it is active
(delete-forward-char).

C-d

Delete the character after point (delete-char).

C-k

Kill to the end of the line (kill-line).

M-d

Kill forward to the end of the next word (kill-word).

M-DEL

Kill back to the beginning of the previous word
(backward-kill-word).

The DEL (delete-backward-char) command removes
the character before point, moving the cursor and the characters after
it backwards. If point was at the beginning of a line, this deletes
the preceding newline, joining this line to the previous one.

If, however, the region is active, DEL instead deletes
the text in the region. See Mark, for a description of the region.

On most keyboards, DEL is labeled BACKSPACE, but we
refer to it as DEL in this manual. (Do not confuse DEL
with the Delete key; we will discuss Delete momentarily.)
On some text terminals, Emacs may not recognize the DEL key
properly. See DEL Does Not Delete, if you encounter this problem.

The Delete (delete-forward-char) command deletes in the
“opposite direction”: it deletes the character after point, i.e., the
character under the cursor. If point was at the end of a line, this
joins the following line onto this one. Like DEL, it
deletes the text in the region if the region is active (see Mark).

C-d (delete-char) deletes the character after point,
similar to Delete, but regardless of whether the region is
active.

See Deletion, for more detailed information about the above
deletion commands.

C-k (kill-line) erases (kills) a line at a time. If
you type C-k at the beginning or middle of a line, it kills all
the text up to the end of the line. If you type C-k at the end
of a line, it joins that line with the following line.

7.4 Undoing Changes

C-/

Undo one entry of the undo records—usually, one command worth
(undo).

C-x u

C-_

The same.

Emacs records a list of changes made in the buffer text, so you can
undo recent changes. This is done using the undo command,
which is bound to C-/ (as well as C-x u and C-_).
Normally, this command undoes the last change, moving point back to
where it was before the change. The undo command applies only to
changes in the buffer; you can’t use it to undo cursor motion.

Although each editing command usually makes a separate entry in the
undo records, very simple commands may be grouped together.
Sometimes, an entry may cover just part of a complex command.

If you repeat C-/ (or its aliases), each repetition undoes
another, earlier change, back to the limit of the undo information
available. If all recorded changes have already been undone, the undo
command displays an error message and does nothing.

7.5 Files

Text that you insert in an Emacs buffer lasts only as long as the
Emacs session. To keep any text permanently, you must put it in a
file.

Suppose there is a file named test.emacs in your home
directory. To begin editing this file in Emacs, type

C-x C-f test.emacs RET

Here the file name is given as an argument to the command C-x
C-f (find-file). That command uses the minibuffer to
read the argument, and you type RET to terminate the argument
(see Minibuffer).

Emacs obeys this command by visiting the file: it creates a
buffer, copies the contents of the file into the buffer, and then
displays the buffer for editing. If you alter the text, you can
save the new text in the file by typing C-x C-s
(save-buffer). This copies the altered buffer contents back
into the file test.emacs, making them permanent. Until you
save, the changed text exists only inside Emacs, and the file
test.emacs is unaltered.

To create a file, just visit it with C-x C-f as if it already
existed. This creates an empty buffer, in which you can insert the
text you want to put in the file. Emacs actually creates the file the
first time you save this buffer with C-x C-s.

7.7 Blank Lines

Here are special commands and techniques for inserting and deleting
blank lines.

C-o

Insert a blank line after the cursor (open-line).

C-x C-o

Delete all but one of many consecutive blank lines
(delete-blank-lines).

We have seen how RET (newline) starts a new line
of text. However, it may be easier to see what you are doing if you
first make a blank line and then insert the desired text into it.
This is easy to do using the key C-o (open-line), which
inserts a newline after point but leaves point in front of the
newline. After C-o, type the text for the new line.

You can make several blank lines by typing C-o several times, or
by giving it a numeric argument specifying how many blank lines to make.
See Arguments, for how. If you have a fill prefix, the C-o
command inserts the fill prefix on the new line, if typed at the
beginning of a line. See Fill Prefix.

The easy way to get rid of extra blank lines is with the command
C-x C-o (delete-blank-lines). If point lies within a run
of several blank lines, C-x C-o deletes all but one of them. If
point is on a single blank line, C-x C-o deletes it. If point
is on a nonblank line, C-x C-o deletes all following blank
lines, if any exists.

7.8 Continuation Lines

Sometimes, a line of text in the buffer—a logical line—is
too long to fit in the window, and Emacs displays it as two or more
screen lines. This is called line wrapping or
continuation, and the long logical line is called a
continued line. On a graphical display, Emacs indicates line
wrapping with small bent arrows in the left and right window fringes.
On a text terminal, Emacs indicates line wrapping by displaying a
‘\’ character at the right margin.

Most commands that act on lines act on logical lines, not screen
lines. For instance, C-k kills a logical line. As described
earlier, C-n (next-line) and C-p
(previous-line) are special exceptions: they move point down
and up, respectively, by one screen line (see Moving Point).

Emacs can optionally truncate long logical lines instead of
continuing them. This means that every logical line occupies a single
screen line; if it is longer than the width of the window, the rest of
the line is not displayed. On a graphical display, a truncated line
is indicated by a small straight arrow in the right fringe; on a text
terminal, it is indicated by a ‘$’ character in the right margin.
See Line Truncation.

By default, continued lines are wrapped at the right window edge.
Since the wrapping may occur in the middle of a word, continued lines
can be difficult to read. The usual solution is to break your lines
before they get too long, by inserting newlines. If you prefer, you
can make Emacs insert a newline automatically when a line gets too
long, by using Auto Fill mode. See Filling.

Sometimes, you may need to edit files containing many long logical
lines, and it may not be practical to break them all up by adding
newlines. In that case, you can use Visual Line mode, which enables
word wrapping: instead of wrapping long lines exactly at the
right window edge, Emacs wraps them at the word boundaries (i.e.,
space or tab characters) nearest to the right window edge. Visual
Line mode also redefines editing commands such as C-a,
C-n, and C-k to operate on screen lines rather than
logical lines. See Visual Line Mode.

M-x what-line displays the current line number in the echo
area. This command is usually redundant, because the current line
number is shown in the mode line (see Mode Line). However, if you
narrow the buffer, the mode line shows the line number relative to
the accessible portion (see Narrowing). By contrast,
what-line displays both the line number relative to the
narrowed region and the line number relative to the whole buffer.

M-= (count-words-region) displays a message reporting
the number of lines, words, and characters in the region
(see Mark, for an explanation of the region). With a prefix
argument, C-u M-=, the command displays a count for the entire
buffer.

The command M-x count-words does the same job, but with a
different calling convention. It displays a count for the region if
the region is active, and for the buffer otherwise.

The command C-x = (what-cursor-position) shows
information about the current cursor position and the buffer contents
at that position. It displays a line in the echo area that looks like
this:

Char: c (99, #o143, #x63) point=28062 of 36168 (78%) column=53

After ‘Char:’, this shows the character in the buffer at point.
The text inside the parenthesis shows the corresponding decimal, octal
and hex character codes; for more information about how C-x =
displays character information, see International Chars. After
‘point=’ is the position of point as a character count (the first
character in the buffer is position 1, the second character is
position 2, and so on). The number after that is the total number of
characters in the buffer, and the number in parenthesis expresses the
position as a percentage of the total. After ‘column=’ is the
horizontal position of point, in columns counting from the left edge
of the window.

If the buffer has been narrowed, making some of the text at the
beginning and the end temporarily inaccessible, C-x = displays
additional text describing the currently accessible range. For
example, it might display this:

Char: C (67, #o103, #x43) point=252 of 889 (28%) <231-599> column=0

where the two extra numbers give the smallest and largest character
position that point is allowed to assume. The characters between
those two positions are the accessible ones. See Narrowing.

7.10 Numeric Arguments

In the terminology of mathematics and computing, argument
means “data provided to a function or operation”. You can give any
Emacs command a numeric argument (also called a prefix
argument). Some commands interpret the argument as a repetition
count. For example, giving C-f an argument of ten causes it to
move point forward by ten characters instead of one. With these
commands, no argument is equivalent to an argument of one, and
negative arguments cause them to move or act in the opposite
direction.

The easiest way to specify a numeric argument is to type a digit
and/or a minus sign while holding down the META key. For
example,

M-5 C-n

moves down five lines. The keys M-1, M-2, and so on, as
well as M--, are bound to commands (digit-argument and
negative-argument) that set up an argument for the next
command. M-- without digits normally means -1.

If you enter more than one digit, you need not hold down the
META key for the second and subsequent digits. Thus, to move
down fifty lines, type

M-5 0 C-n

Note that this does not insert five copies of ‘0’ and move
down one line, as you might expect—the ‘0’ is treated as part
of the prefix argument.

(What if you do want to insert five copies of ‘0’? Type M-5
C-u 0. Here, C-u “terminates” the prefix argument, so that
the next keystroke begins the command that you want to execute. Note
that this meaning of C-u applies only to this case. For the
usual role of C-u, see below.)

Instead of typing M-1, M-2, and so on, another way to
specify a numeric argument is to type C-u
(universal-argument) followed by some digits, or (for a
negative argument) a minus sign followed by digits. A minus sign
without digits normally means -1.

C-u alone has the special meaning of “four times”: it
multiplies the argument for the next command by four. C-u C-u
multiplies it by sixteen. Thus, C-u C-u C-f moves forward
sixteen characters. Other useful combinations are C-u C-n,
C-u C-u C-n (move down a good fraction of a screen), C-u
C-u C-o (make “a lot” of blank lines), and C-u C-k (kill four
lines).

You can use a numeric argument before a self-inserting character to
insert multiple copies of it. This is straightforward when the
character is not a digit; for example, C-u 6 4 a inserts 64
copies of the character ‘a’. But this does not work for
inserting digits; C-u 6 4 1 specifies an argument of 641. You
can separate the argument from the digit to insert with another
C-u; for example, C-u 6 4 C-u 1 does insert 64 copies of
the character ‘1’.

Some commands care whether there is an argument, but ignore its
value. For example, the command M-q (fill-paragraph)
fills text; with an argument, it justifies the text as well.
(See Filling, for more information on M-q.) For these
commands, it is enough to specify the argument with a single
C-u.

Some commands use the value of the argument as a repeat count, but
do something special when there is no argument. For example, the
command C-k (kill-line) with argument n kills
n lines, including their terminating newlines. But C-k
with no argument is special: it kills the text up to the next newline,
or, if point is right at the end of the line, it kills the newline
itself. Thus, two C-k commands with no arguments can kill a
nonblank line, just like C-k with an argument of one.
(See Killing, for more information on C-k.)

A few commands treat a plain C-u differently from an ordinary
argument. A few others may treat an argument of just a minus sign
differently from an argument of -1. These unusual cases are
described when they come up; they exist to make an individual command
more convenient, and they are documented in that command’s
documentation string.

We use the term prefix argument to emphasize that you type
such arguments before the command, and to distinguish them from
minibuffer arguments (see Minibuffer), which are entered after
invoking the command.

7.11 Repeating a Command

Many simple commands, such as those invoked with a single key or
with M-x command-nameRET, can be repeated by
invoking them with a numeric argument that serves as a repeat count
(see Arguments). However, if the command you want to repeat
prompts for input, or uses a numeric argument in another way, that
method won’t work.

The command C-x z (repeat) provides another way to repeat
an Emacs command many times. This command repeats the previous Emacs
command, whatever that was. Repeating a command uses the same arguments
that were used before; it does not read new arguments each time.

To repeat the command more than once, type additional z’s: each
z repeats the command one more time. Repetition ends when you
type a character other than z, or press a mouse button.

For example, suppose you type C-u 2 0 C-d to delete 20
characters. You can repeat that command (including its argument) three
additional times, to delete a total of 80 characters, by typing C-x
z z z. The first C-x z repeats the command once, and each
subsequent z repeats it once again.

8 The Minibuffer

The minibuffer is where Emacs commands read complicated
arguments, such as file names, buffer names, Emacs command names, or
Lisp expressions. We call it the “minibuffer” because it’s a
special-purpose buffer with a small amount of screen space. You can
use the usual Emacs editing commands in the minibuffer to edit the
argument text.

8.1 Using the Minibuffer

When the minibuffer is in use, it appears in the echo area, with a
cursor. The minibuffer starts with a prompt, usually ending
with a colon. The prompt states what kind of input is expected, and
how it will be used. The prompt is highlighted using the
minibuffer-prompt face (see Faces).

The simplest way to enter a minibuffer argument is to type the text,
then RET to submit the argument and exit the minibuffer.
Alternatively, you can type C-g to exit the minibuffer by
canceling the command asking for the argument (see Quitting).

Sometimes, the prompt shows a default argument, inside
parentheses before the colon. This default will be used as the
argument if you just type RET. For example, commands that read
buffer names usually show a buffer name as the default; you can type
RET to operate on that default buffer.

If you enable Minibuffer Electric Default mode, a global minor mode,
Emacs hides the default argument as soon as you modify the contents of
the minibuffer (since typing RET would no longer submit that
default). If you ever bring back the original minibuffer text, the
prompt again shows the default. Furthermore, if you change the
variable minibuffer-eldef-shorten-default to a non-nil
value, the default argument is displayed as ‘[default]’
instead of ‘(default default)’, saving some screen space.
To enable this minor mode, type M-x
minibuffer-electric-default-mode.

Since the minibuffer appears in the echo area, it can conflict with
other uses of the echo area. If an error message or an informative
message is emitted while the minibuffer is active, the message hides
the minibuffer for a few seconds, or until you type something; then
the minibuffer comes back. While the minibuffer is in use, keystrokes
do not echo.

8.2 Minibuffers for File Names

Commands such as C-x C-f (find-file) use the minibuffer
to read a file name argument (see Basic Files). When the
minibuffer is used to read a file name, it typically starts out with
some initial text ending in a slash. This is the default
directory. For example, it may start out like this:

Find file: /u2/emacs/src/

Here, ‘Find file: ’ is the prompt and ‘/u2/emacs/src/’ is
the default directory. If you now type buffer.c as input, that
specifies the file /u2/emacs/src/buffer.c. See File Names,
for information about the default directory.

You can specify the parent directory with ..:
/a/b/../foo.el is equivalent to /a/foo.el.
Alternatively, you can use M-DEL to kill directory names
backwards (see Words).

To specify a file in a completely different directory, you can kill
the entire default with C-a C-k (see Minibuffer Edit).
Alternatively, you can ignore the default, and enter an absolute file
name starting with a slash or a tilde after the default directory.
For example, you can specify /etc/termcap as follows:

Find file: /u2/emacs/src//etc/termcap

Emacs interprets a double slash as “ignore everything before the
second slash in the pair”. In the example above,
/u2/emacs/src/ is ignored, so the argument you supplied is
/etc/termcap. The ignored part of the file name is dimmed if
the terminal allows it. (To disable this dimming, turn off File Name
Shadow mode with the command M-x file-name-shadow-mode.)

Emacs interprets ~/ as your home directory. Thus,
~/foo/bar.txt specifies a file named bar.txt, inside a
directory named foo, which is in turn located in your home
directory. In addition, ~user-id/ means the home
directory of a user whose login name is user-id. Any leading
directory name in front of the ~ is ignored: thus,
/u2/emacs/~/foo/bar.txt is equivalent to ~/foo/bar.txt.

On MS-Windows and MS-DOS systems, where a user doesn’t always have a
home directory, Emacs uses several alternatives. For MS-Windows, see
Windows HOME; for MS-DOS, see
MS-DOS File Names.
On these systems, the ~user-id/ construct is supported
only for the current user, i.e., only if user-id is the current
user’s login name.

To prevent Emacs from inserting the default directory when reading
file names, change the variable insert-default-directory to
nil. In that case, the minibuffer starts out empty.
Nonetheless, relative file name arguments are still interpreted based
on the same default directory.

You can also enter remote file names in the minibuffer.
See Remote Files.

8.3 Editing in the Minibuffer

The minibuffer is an Emacs buffer, albeit a peculiar one, and the
usual Emacs commands are available for editing the argument text.
(The prompt, however, is read-only, and cannot be changed.)

Since RET in the minibuffer submits the argument, you can’t
use it to insert a newline. You can do that with C-q C-j, which
inserts a C-j control character, which is formally equivalent to
a newline character (see Inserting Text). Alternatively, you can
use the C-o (open-line) command (see Blank Lines).

Inside a minibuffer, the keys TAB, SPC, and ? are
often bound to completion commands, which allow you to easily
fill in the desired text without typing all of it. See Completion.
As with RET, you can use C-q to insert a TAB,
SPC, or ‘?’ character.

For convenience, C-a (move-beginning-of-line) in a
minibuffer moves point to the beginning of the argument text, not the
beginning of the prompt. For example, this allows you to erase the
entire argument with C-a C-k.

When the minibuffer is active, the echo area is treated much like an
ordinary Emacs window. For instance, you can switch to another window
(with C-x o), edit text there, then return to the minibuffer
window to finish the argument. You can even kill text in another
window, return to the minibuffer window, and yank the text into the
argument. There are some restrictions on the minibuffer window,
however: for instance, you cannot split it. See Windows.

Normally, the minibuffer window occupies a single screen line.
However, if you add two or more lines’ worth of text into the
minibuffer, it expands automatically to accommodate the text. The
variable resize-mini-windows controls the resizing of the
minibuffer. The default value is grow-only, which means the
behavior we have just described. If the value is t, the
minibuffer window will also shrink automatically if you remove some
lines of text from the minibuffer, down to a minimum of one screen
line. If the value is nil, the minibuffer window never changes
size automatically, but you can use the usual window-resizing commands
on it (see Windows).

The variable max-mini-window-height controls the maximum
height for resizing the minibuffer window. A floating-point number
specifies a fraction of the frame’s height; an integer specifies the
maximum number of lines; nil means do not resize the minibuffer
window automatically. The default value is 0.25.

The C-M-v command in the minibuffer scrolls the help text from
commands that display help text of any sort in another window. You
can also scroll the help text with M-prior and
M-next (or, equivalently, M-PageUp and
M-PageDown). This is especially useful with long lists of
possible completions. See Other Window.

Emacs normally disallows most commands that use the minibuffer while
the minibuffer is active. To allow such commands in the minibuffer,
set the variable enable-recursive-minibuffers to t.

When not active, the minibuffer is in minibuffer-inactive-mode,
and clicking Mouse-1 there shows the *Messages* buffer.
If you use a dedicated frame for minibuffers, Emacs also recognizes
certain keys there, for example n to make a new frame.

8.4 Completion

You can often use a feature called completion to help enter
arguments. This means that after you type part of the argument, Emacs
can fill in the rest, or some of it, based on what was typed so far.

When completion is available, certain keys (usually TAB,
RET, and SPC) are rebound in the minibuffer to special
completion commands (see Completion Commands). These commands
attempt to complete the text in the minibuffer, based on a set of
completion alternatives provided by the command that requested
the argument. You can usually type ? to see a list of
completion alternatives.

Although completion is usually done in the minibuffer, the feature
is sometimes available in ordinary buffers too. See Symbol Completion.

8.4.1 Completion Example

A simple example may help here. M-x uses the minibuffer to
read the name of a command, so completion works by matching the
minibuffer text against the names of existing Emacs commands. Suppose
you wish to run the command auto-fill-mode. You can do that by
typing M-x auto-fill-mode RET, but it is easier to use
completion.

If you type M-x a u TAB, the TAB looks for
completion alternatives (in this case, command names) that start with
‘au’. There are several, including auto-fill-mode and
autoconf-mode, but they all begin with auto, so the
‘au’ in the minibuffer completes to ‘auto’. (More commands
may be defined in your Emacs session. For example, if a command
called authorize-me was defined, Emacs could only complete
as far as ‘aut’.)

If you type TAB again immediately, it cannot determine the
next character; it could be ‘-’, ‘a’, or ‘c’. So it
does not add any characters; instead, TAB displays a list of all
possible completions in another window.

Next, type -f. The minibuffer now contains ‘auto-f’, and
the only command name that starts with this is auto-fill-mode.
If you now type TAB, completion fills in the rest of the
argument ‘auto-fill-mode’ into the minibuffer.

8.4.2 Completion Commands

Here is a list of the completion commands defined in the minibuffer
when completion is allowed.

TAB

Complete the text in the minibuffer as much as possible; if unable to
complete, display a list of possible completions
(minibuffer-complete).

SPC

Complete up to one word from the minibuffer text before point
(minibuffer-complete-word). This command is not available for
arguments that often include spaces, such as file names.

RET

Submit the text in the minibuffer as the argument, possibly completing
first (minibuffer-complete-and-exit). See Completion Exit.

?

Display a list of completions (minibuffer-completion-help).

TAB (minibuffer-complete) is the most fundamental
completion command. It searches for all possible completions that
match the existing minibuffer text, and attempts to complete as much
as it can. See Completion Styles, for how completion alternatives
are chosen.

SPC (minibuffer-complete-word) completes like
TAB, but only up to the next hyphen or space. If you have
‘auto-f’ in the minibuffer and type SPC, it finds that the
completion is ‘auto-fill-mode’, but it only inserts ‘ill-’,
giving ‘auto-fill-’. Another SPC at this point completes
all the way to ‘auto-fill-mode’.

If TAB or SPC is unable to complete, it displays a list
of matching completion alternatives (if there are any) in another
window. You can display the same list with ?
(minibuffer-completion-help). The following commands can be
used with the completion list:

Mouse-1

Mouse-2

Clicking mouse button 1 or 2 on a completion alternative chooses it
(mouse-choose-completion).

M-v

PageUp

prior

Typing M-v, while in the minibuffer, selects the window showing
the completion list (switch-to-completions). This paves the
way for using the commands below. PageUp or prior does
the same. You can also select the window in other ways
(see Windows).

RET

While in the completion list buffer, this chooses the completion at
point (choose-completion).

RIGHT

While in the completion list buffer, this moves point to the following
completion alternative (next-completion).

LEFT

While in the completion list buffer, this moves point to the previous
completion alternative (previous-completion).

8.4.3 Completion Exit

When a command reads an argument using the minibuffer with
completion, it also controls what happens when you type RET
(minibuffer-complete-and-exit) to submit the argument. There
are four types of behavior:

Strict completion accepts only exact completion matches. Typing
RET exits the minibuffer only if the minibuffer text is an exact
match, or completes to one. Otherwise, Emacs refuses to exit the
minibuffer; instead it tries to complete, and if no completion can be
done it momentarily displays ‘[No match]’ after the minibuffer
text. (You can still leave the minibuffer by typing C-g to
cancel the command.)

An example of a command that uses this behavior is M-x, since it
is meaningless for it to accept a non-existent command name.

Cautious completion is like strict completion, except RET
exits only if the text is already an exact match. If the text
completes to an exact match, RET performs that completion but
does not exit yet; you must type a second RET to exit.

Cautious completion is used for reading file names for files that must
already exist, for example.

Permissive completion allows any input; the completion
candidates are just suggestions. Typing RET does not complete,
it just submits the argument as you have entered it.

Permissive completion with confirmation is like permissive
completion, with an exception: if you typed TAB and this
completed the text up to some intermediate state (i.e., one that is not
yet an exact completion match), typing RET right afterward does
not submit the argument. Instead, Emacs asks for confirmation by
momentarily displaying ‘[Confirm]’ after the text; type RET
again to confirm and submit the text. This catches a common mistake,
in which one types RET before realizing that TAB did not
complete as far as desired.

You can tweak the confirmation behavior by customizing the variable
confirm-nonexistent-file-or-buffer. The default value,
after-completion, gives the behavior we have just described.
If you change it to nil, Emacs does not ask for confirmation,
falling back on permissive completion. If you change it to any other
non-nil value, Emacs asks for confirmation whether or not the
preceding command was TAB.

This behavior is used by most commands that read file names, like
C-x C-f, and commands that read buffer names, like C-x b.

8.4.4 How Completion Alternatives Are Chosen

Completion commands work by narrowing a large list of possible
completion alternatives to a smaller subset that “matches” what you
have typed in the minibuffer. In Completion Example, we gave a
simple example of such matching. The procedure of determining what
constitutes a “match” is quite intricate. Emacs attempts to offer
plausible completions under most circumstances.

Emacs performs completion using one or more completion
styles—sets of criteria for matching minibuffer text to completion
alternatives. During completion, Emacs tries each completion style in
turn. If a style yields one or more matches, that is used as the list
of completion alternatives. If a style produces no matches, Emacs
falls back on the next style.

The list variable completion-styles specifies the completion
styles to use. Each list element is the name of a completion style (a
Lisp symbol). The default completion styles are (in order):

basic

A matching completion alternative must have the same beginning as the
text in the minibuffer before point. Furthermore, if there is any
text in the minibuffer after point, the rest of the completion
alternative must contain that text as a substring.

partial-completion

This aggressive completion style divides the minibuffer text into
words separated by hyphens or spaces, and completes each word
separately. (For example, when completing command names,
‘em-l-m’ completes to ‘emacs-lisp-mode’.)

Furthermore, a ‘*’ in the minibuffer text is treated as a
wildcard—it matches any character at the corresponding
position in the completion alternative.

emacs22

This completion style is similar to basic, except that it
ignores the text in the minibuffer after point. It is so-named
because it corresponds to the completion behavior in Emacs 22.

The following additional completion styles are also defined, and you
can add them to completion-styles if you wish
(see Customization):

substring

A matching completion alternative must contain the text in the
minibuffer before point, and the text in the minibuffer after point,
as substrings (in that same order).

Thus, if the text in the minibuffer is ‘foobar’, with point
between ‘foo’ and ‘bar’, that matches
‘afoobbarc’, where a, b, and
c can be any string including the empty string.

initials

This very aggressive completion style attempts to complete acronyms
and initialisms. For example, when completing command names, it
matches ‘lch’ to ‘list-command-history’.

There is also a very simple completion style called emacs21.
In this style, if the text in the minibuffer is ‘foobar’,
only matches starting with ‘foobar’ are considered.

You can use different completion styles in different situations,
by setting the variable completion-category-overrides.
For example, the default setting says to use only basic
and substring completion for buffer names.

8.4.5 Completion Options

Case is significant when completing case-sensitive arguments, such
as command names. For example, when completing command names,
‘AU’ does not complete to ‘auto-fill-mode’. Case
differences are ignored when completing arguments in which case does
not matter.

When completing file names, case differences are ignored if the
variable read-file-name-completion-ignore-case is
non-nil. The default value is nil on systems that have
case-sensitive file-names, such as GNU/Linux; it is non-nil on
systems that have case-insensitive file-names, such as Microsoft
Windows. When completing buffer names, case differences are ignored
if the variable read-buffer-completion-ignore-case is
non-nil; the default is nil.

When completing file names, Emacs usually omits certain alternatives
that are considered unlikely to be chosen, as determined by the list
variable completion-ignored-extensions. Each element in the
list should be a string; any file name ending in such a string is
ignored as a completion alternative. Any element ending in a slash
(/) represents a subdirectory name. The standard value of
completion-ignored-extensions has several elements including
".o", ".elc", and "~". For example, if a
directory contains ‘foo.c’ and ‘foo.elc’, ‘foo’
completes to ‘foo.c’. However, if all possible
completions end in “ignored” strings, they are not ignored: in the
previous example, ‘foo.e’ completes to ‘foo.elc’. Emacs
disregards completion-ignored-extensions when showing
completion alternatives in the completion list.

Shell completion is an extended version of filename completion,
see Shell Options.

If completion-auto-help is set to nil, the completion
commands never display the completion list buffer; you must type
? to display the list. If the value is lazy, Emacs only
shows the completion list buffer on the second attempt to complete.
In other words, if there is nothing to complete, the first TAB
echoes ‘Next char not unique’; the second TAB shows the
completion list buffer.

If completion-cycle-threshold is non-nil, completion
commands can “cycle” through completion alternatives. Normally, if
there is more than one completion alternative for the text in the
minibuffer, a completion command completes up to the longest common
substring. If you change completion-cycle-threshold to
t, the completion command instead completes to the first of
those completion alternatives; each subsequent invocation of the
completion command replaces that with the next completion alternative,
in a cyclic manner. If you give completion-cycle-threshold a
numeric value n, completion commands switch to this cycling
behavior only when there are n or fewer alternatives.

8.5 Minibuffer History

Every argument that you enter with the minibuffer is saved in a
minibuffer history list so you can easily use it again later.
You can use the following arguments to quickly fetch an earlier
argument into the minibuffer:

M-p

UP

Move to the previous item in the minibuffer history, an earlier
argument (previous-history-element).

M-n

DOWN

Move to the next item in the minibuffer history
(next-history-element).

M-r regexpRET

Move to an earlier item in the minibuffer history that
matches regexp (previous-matching-history-element).

M-s regexpRET

Move to a later item in the minibuffer history that matches
regexp (next-matching-history-element).

While in the minibuffer, M-p or UP
(previous-history-element) moves through the minibuffer history
list, one item at a time. Each M-p fetches an earlier item from
the history list into the minibuffer, replacing its existing contents.
Typing M-n or DOWN (next-history-element) moves
through the minibuffer history list in the opposite direction,
fetching later entries into the minibuffer.

If you type M-n in the minibuffer when there are no later
entries in the minibuffer history (e.g., if you haven’t previously
typed M-p), Emacs tries fetching from a list of default
arguments: values that you are likely to enter. You can think of this
as moving through the “future history” list.

If you edit the text inserted by the M-p or M-n
minibuffer history commands, this does not change its entry in the
history list. However, the edited argument does go at the end of the
history list when you submit it.

You can use M-r (previous-matching-history-element) to
search through older elements in the history list, and M-s
(next-matching-history-element) to search through newer
entries. Each of these commands asks for a regular expression
as an argument, and fetches the first matching entry into the
minibuffer. See Regexps, for an explanation of regular
expressions. A numeric prefix argument n means to fetch the
nth matching entry. These commands are unusual, in that they
use the minibuffer to read the regular expression argument, even
though they are invoked from the minibuffer. An upper-case letter in
the regular expression makes the search case-sensitive (see Search Case).

You can also search through the history using an incremental search.
See Isearch Minibuffer.

Emacs keeps separate history lists for several different kinds of
arguments. For example, there is a list for file names, used by all
the commands that read file names. Other history lists include buffer
names, command names (used by M-x), and command arguments (used
by commands like query-replace).

The variable history-length specifies the maximum length of a
minibuffer history list; adding a new element deletes the oldest
element if the list gets too long. If the value is t, there is
no maximum length.

The variable history-delete-duplicates specifies whether to
delete duplicates in history. If it is non-nil, adding a new
element deletes from the list all other elements that are equal to it.
The default is nil.

8.6 Repeating Minibuffer Commands

Every command that uses the minibuffer once is recorded on a special
history list, the command history, together with the values of
its arguments, so that you can repeat the entire command. In
particular, every use of M-x is recorded there, since M-x
uses the minibuffer to read the command name.

C-x ESCESC

Re-execute a recent minibuffer command from the command history
(repeat-complex-command).

M-x list-command-history

Display the entire command history, showing all the commands
C-x ESCESC can repeat, most recent first.

C-x ESCESC re-executes a recent command that used
the minibuffer. With no argument, it repeats the last such command.
A numeric argument specifies which command to repeat; 1 means the last
one, 2 the previous, and so on.

C-x ESCESC works by turning the previous command
into a Lisp expression and then entering a minibuffer initialized with
the text for that expression. Even if you don’t know Lisp, it will
probably be obvious which command is displayed for repetition. If you
type just RET, that repeats the command unchanged. You can also
change the command by editing the Lisp expression before you execute
it. The executed command is added to the front of the command history
unless it is identical to the most recent item.

Once inside the minibuffer for C-x ESCESC, you
can use the usual minibuffer history commands (see Minibuffer History) to move through the history list. After finding the desired
previous command, you can edit its expression as usual and then execute
it by typing RET.

Incremental search does not, strictly speaking, use the minibuffer.
Therefore, although it behaves like a complex command, it normally
does not appear in the history list for C-x ESCESC.
You can make incremental search commands appear in the history by
setting isearch-resume-in-command-history to a non-nil
value. See Incremental Search.

The list of previous minibuffer-using commands is stored as a Lisp
list in the variable command-history. Each element is a Lisp
expression that describes one command and its arguments. Lisp programs
can re-execute a command by calling eval with the
command-history element.

8.7 Entering passwords

Sometimes, you may need to enter a password into Emacs. For instance,
when you tell Emacs to visit a file on another machine via a network
protocol such as FTP, you often need to supply a password to gain
access to the machine (see Remote Files).

Entering a password is similar to using a minibuffer. Emacs
displays a prompt in the echo area (such as ‘Password: ’); after
you type the required password, press RET to submit it. To
prevent others from seeing your password, every character you type is
displayed as a dot (‘.’) instead of its usual form.

Most of the features and commands associated with the minibuffer can
not be used when entering a password. There is no history or
completion, and you cannot change windows or perform any other action
with Emacs until you have submitted the password.

While you are typing the password, you may press DEL to delete
backwards, removing the last character entered. C-u deletes
everything you have typed so far. C-g quits the password prompt
(see Quitting). C-y inserts the current kill into the
password (see Killing). You may type either RET or
ESC to submit the password. Any other self-inserting character
key inserts the associated character into the password, and all other
input is ignored.

8.8 Yes or No Prompts

An Emacs command may require you to answer a “yes or no” question
during the course of its execution. Such queries come in two main
varieties.

For the first type of “yes or no” query, the prompt ends with
‘(y or n)’. Such a query does not actually use the minibuffer;
the prompt appears in the echo area, and you answer by typing either
‘y’ or ‘n’, which immediately delivers the response. For
example, if you type C-x C-w (write-file) to save a
buffer, and enter the name of an existing file, Emacs issues a prompt
like this:

File `foo.el' exists; overwrite? (y or n)

Because this query does not actually use the minibuffer, the usual
minibuffer editing commands cannot be used. However, you can perform
some window scrolling operations while the query is active: C-l
recenters the selected window; M-v (or PageDown or
next) scrolls forward; C-v (or PageUp, or
prior) scrolls backward; C-M-v scrolls forward in the next
window; and C-M-S-v scrolls backward in the next window. Typing
C-g dismisses the query, and quits the command that issued it
(see Quitting).

The second type of “yes or no” query is typically employed if
giving the wrong answer would have serious consequences; it uses the
minibuffer, and features a prompt ending with ‘(yes or no)’. For
example, if you invoke C-x k (kill-buffer) on a
file-visiting buffer with unsaved changes, Emacs activates the
minibuffer with a prompt like this:

Buffer foo.el modified; kill anyway? (yes or no)

To answer, you must type ‘yes’ or ‘no’ into the minibuffer,
followed by RET. The minibuffer behaves as described in the
previous sections; you can switch to another window with C-x o,
use the history commands M-p and M-f, etc. Type C-g
to quit the minibuffer and the querying command.

9 Running Commands by Name

Every Emacs command has a name that you can use to run it. For
convenience, many commands also have key bindings. You can run those
commands by typing the keys, or run them by name. Most Emacs commands
have no key bindings, so the only way to run them is by name.
(See Key Bindings, for how to set up key bindings.)

By convention, a command name consists of one or more words,
separated by hyphens; for example, auto-fill-mode or
manual-entry. Command names mostly use complete English words
to make them easier to remember.

To run a command by name, start with M-x, type the command
name, then terminate it with RET. M-x uses the minibuffer
to read the command name. The string ‘M-x’ appears at the
beginning of the minibuffer as a prompt to remind you to enter a
command name to be run. RET exits the minibuffer and runs the
command. See Minibuffer, for more information on the minibuffer.

You can use completion to enter the command name. For example,
to invoke the command forward-char, you can type

M-x forward-char RET

or

M-x forw TAB c RET

Note that forward-char is the same command that you invoke with
the key C-f. The existence of a key binding does not stop you
from running the command by name.

To cancel the M-x and not run a command, type C-g instead
of entering the command name. This takes you back to command level.

To pass a numeric argument to the command you are invoking with
M-x, specify the numeric argument before M-x. The
argument value appears in the prompt while the command name is being
read, and finally M-x passes the argument to that command.

When the command you run with M-x has a key binding, Emacs
mentions this in the echo area after running the command. For
example, if you type M-x forward-word, the message says that you
can run the same command by typing M-f. You can turn off these
messages by setting the variable suggest-key-bindings to
nil.

In this manual, when we speak of running a command by name, we often
omit the RET that terminates the name. Thus we might say
M-x auto-fill-mode rather than M-x auto-fill-mode
RET. We mention the RET only for emphasis, such as when
the command is followed by arguments.

M-x works by running the command
execute-extended-command, which is responsible for reading the
name of another command and invoking it.

10 Help

Emacs provides a wide variety of help commands, all accessible
through the prefix key C-h (or, equivalently, the function key
F1). These help commands are described in the following
sections. You can also type C-h C-h to view a list of help
commands (help-for-help). You can scroll the list with
SPC and DEL, then type the help command you want. To
cancel, type C-g.

Many help commands display their information in a special help
buffer. In this buffer, you can type SPC and DEL to
scroll and type RET to follow hyperlinks. See Help Mode.

If you are looking for a certain feature, but don’t know what it is
called or where to look, we recommend three methods. First, try an
apropos command, then try searching the manual index, then look in the
FAQ and the package keywords.

C-h a topicsRET

This searches for commands whose names match the argument
topics. The argument can be a keyword, a list of keywords, or a
regular expression (see Regexps). See Apropos.

C-h i d m emacs RET i topicRET

This searches for topic in the indices of the Emacs Info manual,
displaying the first match found. Press , to see subsequent
matches. You can use a regular expression as topic.

C-h i d m emacs RET s topicRET

Similar, but searches the text of the manual rather than the
indices.

C-h C-f

This displays the Emacs FAQ, using Info.

C-h p

This displays the available Emacs packages based on keywords.
See Package Keywords.

C-h or F1 mean “help” in various other contexts as
well. For instance, you can type them after a prefix key to view a
list of the keys that can follow the prefix key. (You can also use
? in this context. A few prefix keys don’t support C-h
or ? in this way, because they define other meanings for those
inputs, but they all support F1.)

Display documentation on the Lisp function named function
(describe-function). Since commands are Lisp functions,
this works for commands too.

C-h h

Display the HELLO file, which shows examples of various character
sets.

C-h i

Run Info, the GNU documentation browser (info). The Emacs
manual is available in Info.

C-h k key

Display the name and documentation of the command that key runs
(describe-key).

C-h l

Display a description of your last 300 keystrokes
(view-lossage).

C-h m

Display documentation of the current major mode (describe-mode).

C-h n

Display news of recent Emacs changes (view-emacs-news).

C-h p

Find packages by topic keyword (finder-by-keyword). This lists
packages using a package menu buffer. See Packages.

C-h P packageRET

Display documentation about the specified package
(describe-package).

C-h r

Display the Emacs manual in Info (info-emacs-manual).

C-h s

Display the contents of the current syntax table
(describe-syntax). The syntax table says which characters are
opening delimiters, which are parts of words, and so on. See Syntax Tables in The Emacs Lisp Reference Manual, for
details.

C-h t

Enter the Emacs interactive tutorial (help-with-tutorial).

C-h v varRET

Display the documentation of the Lisp variable var
(describe-variable).

C-h w commandRET

Show which keys run the command named command (where-is).

C-h C codingRET

Describe the coding system coding
(describe-coding-system).

C-h C RET

Describe the coding systems currently in use.

C-h F commandRET

Enter Info and go to the node that documents the Emacs command
command (Info-goto-emacs-command-node).

C-h I methodRET

Describe the input method method (describe-input-method).

C-h K key

Enter Info and go to the node that documents the key sequence
key (Info-goto-emacs-key-command-node).

C-h L language-envRET

Display information on the character sets, coding systems, and input
methods used in language environment language-env
(describe-language-environment).

C-h S symbolRET

Display the Info documentation on symbol symbol according to the
programming language you are editing (info-lookup-symbol).

C-h .

Display the help message for a special text area, if point is in one
(display-local-help). (These include, for example, links in
*Help* buffers.)

10.2 Documentation for a Key

The help commands to get information about a key sequence are
C-h c (describe-key-briefly) and C-h k
(describe-key).

C-h c key displays in the echo area the name of the
command that key is bound to. For example, C-h c C-f
displays ‘forward-char’.

C-h k key is similar but gives more information: it
displays a help buffer containing the command’s documentation
string, which describes exactly what the command does.

C-h K key displays the section of the Emacs manual that
describes the command corresponding to key.

C-h c, C-h k and C-h K work for any sort of key
sequences, including function keys, menus, and mouse events. For
instance, after C-h k you can select a menu item from the menu
bar, to view the documentation string of the command it runs.

C-h w commandRET lists the keys that are bound to
command. It displays the list in the echo area. If it says the
command is not on any key, that means you must use M-x to run
it. C-h w runs the command where-is.

10.3 Help by Command or Variable Name

C-h f functionRET (describe-function)
displays the documentation of Lisp function function, in a
window. Since commands are Lisp functions, you can use this method to
view the documentation of any command whose name you know. For
example,

C-h f auto-fill-mode RET

displays the documentation of auto-fill-mode. This is the only
way to get the documentation of a command that is not bound to any key
(one which you would normally run using M-x).

C-h f is also useful for Lisp functions that you use in a Lisp
program. For example, if you have just written the expression
(make-vector len) and want to check that you are using
make-vector properly, type C-h f make-vector RET.
Because C-h f allows all function names, not just command names,
you may find that some of your favorite completion abbreviations that
work in M-x don’t work in C-h f. An abbreviation that is
unique among command names may not be unique among all function names.

If you type C-h f RET, it describes the function called
by the innermost Lisp expression in the buffer around point,
provided that function name is a valid, defined Lisp function.
(That name appears as the default while you enter the argument.) For
example, if point is located following the text ‘(make-vector
(car x)’, the innermost list containing point is the one that starts
with ‘(make-vector’, so C-h f RET describes the
function make-vector.

C-h f is also useful just to verify that you spelled a
function name correctly. If the minibuffer prompt for C-h f
shows the function name from the buffer as the default, it means that
name is defined as a Lisp function. Type C-g to cancel the
C-h f command if you don’t really want to view the
documentation.

C-h v (describe-variable) is like C-h f but
describes Lisp variables instead of Lisp functions. Its default is
the Lisp symbol around or before point, if that is the name of a
defined Lisp variable. See Variables.

Help buffers that describe Emacs variables and functions normally
have hyperlinks to the corresponding source code, if you have the
source files installed (see Hyperlinking).

To find a command’s documentation in a manual, use C-h F
(Info-goto-emacs-command-node). This knows about various
manuals, not just the Emacs manual, and finds the right one.

10.4 Apropos

The apropos commands answer questions like, “What are the
commands for working with files?” More precisely, you specify an
apropos pattern, which means either a word, a list of words, or
a regular expression.

Each of the following apropos commands reads an apropos pattern in
the minibuffer, searches for items that match the pattern, and
displays the results in a different window.

C-h a

Search for commands (apropos-command). With a prefix argument,
search for noninteractive functions too.

M-x apropos

Search for functions and variables. Both interactive functions
(commands) and noninteractive functions can be found by this.

M-x apropos-user-option

Search for user-customizable variables. With a prefix argument,
search for non-customizable variables too.

M-x apropos-variable

Search for variables. With a prefix argument, search for
customizable variables only.

M-x apropos-value

Search for variables whose values match the specified pattern. With a
prefix argument, search also for functions with definitions matching
the pattern, and Lisp symbols with properties matching the pattern.

The simplest kind of apropos pattern is one word. Anything
containing that word matches the pattern. Thus, to find commands that
work on files, type C-h a file RET. This displays a list
of all command names that contain ‘file’, including
copy-file, find-file, and so on. Each command name
comes with a brief description and a list of keys you can currently
invoke it with. In our example, it would say that you can invoke
find-file by typing C-x C-f.

For more information about a function definition, variable or symbol
property listed in an apropos buffer, you can click on it with
Mouse-1 or Mouse-2, or move there and type RET.

When you specify more than one word in the apropos pattern, a name
must contain at least two of the words in order to match. Thus, if
you are looking for commands to kill a chunk of text before point, you
could try C-h a kill back backward behind before RET. The
real command name kill-backward will match that; if there were
a command kill-text-before, it would also match, since it
contains two of the specified words.

For even greater flexibility, you can specify a regular expression
(see Regexps). An apropos pattern is interpreted as a regular
expression if it contains any of the regular expression special
characters, ‘^$*+?.\[’.

Following the conventions for naming Emacs commands, here are some
words that you’ll find useful in apropos patterns. By using them in
C-h a, you will also get a feel for the naming conventions.

If the variable apropos-do-all is non-nil, the apropos
commands always behave as if they had been given a prefix argument.

By default, all apropos commands except apropos-documentation
list their results in alphabetical order. If the variable
apropos-sort-by-scores is non-nil, these commands
instead try to guess the relevance of each result, and display the
most relevant ones first. The apropos-documentation command
lists its results in order of relevance by default; to list them in
alphabetical order, change the variable
apropos-documentation-sort-by-scores to nil.

10.5 Help Mode Commands

Help buffers provide the same commands as View mode (see View Mode); for instance, SPC scrolls forward, and DEL or
S-SPC scrolls backward. A few special commands are also
provided:

RET

Follow a cross reference at point (help-follow).

TAB

Move point forward to the next hyperlink (forward-button).

S-TAB

Move point back to the previous hyperlink (backward-button).

Mouse-1

Mouse-2

Follow a hyperlink that you click on.

C-c C-c

Show all documentation about the symbol at point
(help-follow-symbol).

C-c C-b

Go back to the previous help topic (help-go-back).

When a function name, variable name, or face name (see Faces)
appears in the documentation in the help buffer, it is normally an
underlined hyperlink. To view the associated documentation,
move point there and type RET (help-follow), or click on
the hyperlink with Mouse-1 or Mouse-2. Doing so replaces
the contents of the help buffer; to retrace your steps, type C-c
C-b (help-go-back).

A help buffer can also contain hyperlinks to Info manuals, source
code definitions, and URLs (web pages). The first two are opened in
Emacs, and the third using a web browser via the browse-url
command (see Browse-URL).

In a help buffer, TAB (forward-button) moves point
forward to the next hyperlink, while S-TAB
(backward-button) point back to the previous hyperlink. These
commands act cyclically; for instance, typing TAB at the last
hyperlink moves back to the first hyperlink.

To view all documentation about any symbol in the text, move point
to there and type C-c C-c (help-follow-symbol). This
shows all available documentation about the symbol—as a variable,
function and/or face.

10.6 Keyword Search for Packages

Most optional features in Emacs are grouped into packages.
Emacs contains several hundred built-in packages, and more can be
installed over the network (see Packages).

To make it easier to find packages related to a topic, most packages
are associated with one or more keywords based on what they do.
Type C-h p (finder-by-keyword) to bring up a list of
package keywords, together with a description of what the keywords
mean. To view a list of packages for a given keyword, type RET
on that line; this displays the list of packages in a Package Menu
buffer (see Package Menu).

C-h P (describe-package) prompts for the name of a
package, and displays a help buffer describing the attributes of the
package and the features that it implements. The buffer lists the
keywords that relate to the package in the form of buttons. Click on
a button to see other packages related to that keyword.

10.7 Help for International Language Support

For information on a specific language environment (see Language Environments), type C-h L
(describe-language-environment). This displays a help buffer
describing the languages supported by the language environment, and
listing the associated character sets, coding systems, and input
methods, as well as some sample text for that language environment.

The command C-h h (view-hello-file) displays the file
etc/HELLO, which demonstrates various character sets by showing
how to say “hello” in many languages.

The command C-h I (describe-input-method) describes an
input method—either a specified input method, or by default the
input method currently in use. See Input Methods.

The command C-h C (describe-coding-system) describes
coding systems—either a specified coding system, or the ones
currently in use. See Coding Systems.

10.8 Other Help Commands

C-h i (info) runs the Info program, which browses
structured documentation files. The entire Emacs manual is available
within Info, along with many other manuals for the GNU system. Type
h after entering Info to run a tutorial on using Info.

With a numeric argument n, C-h i selects the Info buffer
‘*info*<n>’. This is useful if you want to browse multiple
Info manuals simultaneously. If you specify just C-u as the
prefix argument, C-h i prompts for the name of a documentation
file, so you can browse a file which doesn’t have an entry in the
top-level Info menu.

The help commands C-h F functionRET and C-h
K key, described above, enter Info and go straight to the
documentation of function or key.

When editing a program, if you have an Info version of the manual
for the programming language, you can use C-h S
(info-lookup-symbol) to find an entry for a symbol (keyword,
function or variable) in the proper manual. The details of how this
command works depend on the major mode.

If something surprising happens, and you are not sure what you typed,
use C-h l (view-lossage). C-h l displays your last
300 input keystrokes. If you see commands that you don’t know, you can
use C-h c to find out what they do.

To review recent echo area messages, use C-h e
(view-echo-area-messages). This displays the buffer
*Messages*, where those messages are kept.

Each Emacs major mode typically redefines a few keys and makes other
changes in how editing works. C-h m (describe-mode)
displays documentation on the current major mode, which normally
describes the commands and features that are changed in this mode.

C-h b (describe-bindings) and C-h s
(describe-syntax) show other information about the current
environment within Emacs. C-h b displays a list of all the key
bindings now in effect: first the local bindings of the current minor
modes, then the local bindings defined by the current major mode, and
finally the global bindings (see Key Bindings). C-h s
displays the contents of the syntax table, with explanations of each
character’s syntax (see Syntax Tables in The
Emacs Lisp Reference Manual).

You can get a list of subcommands for a particular prefix key by
typing C-h, ?, or F1
(describe-prefix-bindings) after the prefix key. (There are a
few prefix keys for which not all of these keys work—those that
provide their own bindings for that key. One of these prefix keys
is ESC, because ESC C-h is actually C-M-h,
which marks a defun. However, ESCF1 and
ESC ? work fine.)

10.9 Help Files

Apart from the built-in documentation and manuals, Emacs contains
several other files describing topics like copying conditions, release
notes, instructions for debugging and reporting bugs, and so forth.
You can use the following commands to view these files. Apart from
C-h g, they all have the form C-h C-char.

C-h C-c

Display the rules under which you can copy and redistribute Emacs
(describe-copying).

C-h C-d

Display help for debugging Emacs (view-emacs-debugging).

C-h C-e

Display information about where to get external packages
(view-external-packages).

10.10 Help on Active Text and Tooltips

In Emacs, stretches of “active text” (text that does something
special in response to mouse clicks or RET) often have
associated help text. This includes hyperlinks in Emacs buffers, as
well as parts of the mode line. On graphical displays, as well as
some text terminals which support mouse tracking, moving the mouse
over the active text displays the help text as a tooltip.
See Tooltips.

On terminals that don’t support mouse-tracking, you can display the
help text for active buffer text at point by typing C-h .
(display-local-help). This shows the help text in the echo
area. To display help text automatically whenever it is available at
point, set the variable help-at-pt-display-when-idle to
t.

11 The Mark and the Region

Many Emacs commands operate on an arbitrary contiguous part of the
current buffer. To specify the text for such a command to operate on,
you set the mark at one end of it, and move point to the other
end. The text between point and the mark is called the region.
The region always extends between point and the mark, no matter which
one comes earlier in the text; each time you move point, the region
changes.

Setting the mark at a position in the text also activates it.
When the mark is active, we say also that the region is active; Emacs
indicates its extent by highlighting the text within it, using the
region face (see Face Customization).

After certain non-motion commands, including any command that
changes the text in the buffer, Emacs automatically deactivates
the mark; this turns off the highlighting. You can also explicitly
deactivate the mark at any time, by typing C-g
(see Quitting).

The above default behavior is known as Transient Mark mode.
Disabling Transient Mark mode switches Emacs to an alternative
behavior, in which the region is usually not highlighted.
See Disabled Transient Mark.

Setting the mark in one buffer has no effect on the marks in other
buffers. When you return to a buffer with an active mark, the mark is
at the same place as before. When multiple windows show the same
buffer, they can have different values of point, and thus different
regions, but they all share one common mark position. See Windows.
Ordinarily, only the selected window highlights its region; however,
if the variable highlight-nonselected-windows is
non-nil, each window highlights its own region.

There is another kind of region: the “rectangular region”.
See Rectangles.

11.1 Setting the Mark

Set the mark at point, and activate it; then move point where the mark
used to be (exchange-point-and-mark).

Drag-Mouse-1

Set point and the mark around the text you drag across.

Mouse-3

Set the mark at point, then move point to where you click
(mouse-save-then-kill).

‘Shifted cursor motion keys’

Set the mark at point if the mark is inactive, then move point.
See Shift Selection.

The most common way to set the mark is with C-SPC
(set-mark-command)5. This sets the mark where point is,
and activates it. You can then move point away, leaving the mark
behind.

For example, suppose you wish to convert part of the buffer to upper
case. To accomplish this, go to one end of the desired text, type
C-SPC, and move point until the desired portion of text is
highlighted. Now type C-x C-u (upcase-region). This
converts the text in the region to upper case, and then deactivates
the mark.

Whenever the mark is active, you can deactivate it by typing
C-g (see Quitting). Most commands that operate on the
region also automatically deactivate the mark, like C-x C-u in
the above example.

Instead of setting the mark in order to operate on a region, you can
also use it to “remember” a position in the buffer (by typing
C-SPC C-SPC), and later jump back there (by typing
C-u C-SPC). See Mark Ring, for details.

The command C-x C-x (exchange-point-and-mark) exchanges
the positions of point and the mark. C-x C-x is useful when you
are satisfied with the position of point but want to move the other
end of the region (where the mark is). Using C-x C-x a second
time, if necessary, puts the mark at the new position with point back
at its original position. Normally, if the mark is inactive, this
command first reactivates the mark wherever it was last set, to ensure
that the region is left highlighted. However, if you call it with a
prefix argument, it leaves the mark inactive and the region
unhighlighted; you can use this to jump to the mark in a manner
similar to C-u C-SPC.

You can also set the mark with the mouse. If you press the left
mouse button (down-mouse-1) and drag the mouse across a range of
text, this sets the mark where you first pressed the mouse button and
puts point where you release it. Alternatively, clicking the right
mouse button (mouse-3) sets the mark at point and then moves
point to where you clicked. See Mouse Commands, for a more
detailed description of these mouse commands.

Finally, you can set the mark by holding down the shift key while
typing certain cursor motion commands (such as S-RIGHT,
S-C-f, S-C-n, etc.). This is called shift-selection.
It sets the mark at point before moving point, but only if there is no
active mark set via shift-selection. The mark set by mouse commands
and by shift-selection behaves slightly differently from the usual
mark: any subsequent unshifted cursor motion command deactivates it
automatically. For details, See Shift Selection.

Many commands that insert text, such as C-y (yank), set
the mark at the other end of the inserted text, without activating it.
This lets you easily return to that position (see Mark Ring). You
can tell that a command does this when it shows ‘Mark set’ in the
echo area.

Under X, every time the active region changes, Emacs saves the text
in the region to the primary selection. This lets you insert
that text into other X applications with mouse-2 clicks.
See Primary Selection.

11.2 Commands to Mark Textual Objects

Here are commands for placing point and the mark around a textual
object such as a word, list, paragraph or page:

M-@

Set mark after end of next word (mark-word). This does not
move point.

C-M-@

Set mark after end of following balanced expression
(mark-sexp). This does not move point.

M-h

Move point to the beginning of the current paragraph, and set mark at
the end (mark-paragraph).

C-M-h

Move point to the beginning of the current defun, and set mark at the
end (mark-defun).

C-x C-p

Move point to the beginning of the current page, and set mark at the
end (mark-page).

C-x h

Move point to the beginning of the buffer, and set mark at the end
(mark-whole-buffer).

M-@ (mark-word) sets the mark at the end of the next
word (see Words, for information about words). Repeated
invocations of this command extend the region by advancing the mark
one word at a time. As an exception, if the mark is active and
located before point, M-@ moves the mark backwards from its
current position one word at a time.

This command also accepts a numeric argument n, which tells it
to advance the mark by n words. A negative argument moves the
mark back by n words.

Similarly, C-M-@ (mark-sexp) puts the mark at the end
of the next balanced expression (see Expressions). Repeated
invocations extend the region to subsequent expressions, while
positive or negative numeric arguments move the mark forward or
backward by the specified number of expressions.

The other commands in the above list set both point and mark, so as
to delimit an object in the buffer. M-h (mark-paragraph)
marks paragraphs (see Paragraphs), C-M-h (mark-defun)
marks top-level definitions (see Moving by Defuns), and C-x
C-p (mark-page) marks pages (see Pages). Repeated
invocations again play the same role, extending the region to
consecutive objects; similarly, numeric arguments specify how many
objects to move the mark by.

C-x h (mark-whole-buffer) sets up the entire buffer as
the region, by putting point at the beginning and the mark at the end.

Some commands have a default behavior when the mark is inactive, but
operate on the region if the mark is active. For example, M-$
(ispell-word) normally checks the spelling of the word at
point, but it checks the text in the region if the mark is active
(see Spelling). Normally, such commands use their default
behavior if the region is empty (i.e., if mark and point are at the
same position). If you want them to operate on the empty region,
change the variable use-empty-active-region to t.

As described in Erasing, the DEL
(backward-delete-char) and delete
(delete-forward-char) commands also act this way. If the mark
is active, they delete the text in the region. (As an exception, if
you supply a numeric argument n, where n is not one, these
commands delete n characters regardless of whether the mark is
active). If you change the variable delete-active-region to
nil, then these commands don’t act differently when the mark is
active. If you change the value to kill, these commands
kill the region instead of deleting it (see Killing).

Other commands always operate on the region, and have no default
behavior. Such commands usually have the word region in their
names, like C-w (kill-region) and C-x C-u
(upcase-region). If the mark is inactive, they operate on the
“inactive region”—that is, on the text between point and the
position at which the mark was last set (see Mark Ring). To
disable this behavior, change the variable
mark-even-if-inactive to nil. Then these commands will
instead signal an error if the mark is inactive.

By default, text insertion occurs normally even if the mark is
active—for example, typing a inserts the character ‘a’,
then deactivates the mark. If you enable Delete Selection mode, a
minor mode, then inserting text while the mark is active causes the
text in the region to be deleted first. To toggle Delete Selection
mode on or off, type M-x delete-selection-mode.

11.4 The Mark Ring

Each buffer remembers previous locations of the mark, in the
mark ring. Commands that set the mark also push the old mark
onto this ring. One of the uses of the mark ring is to remember spots
that you may want to go back to.

C-SPC C-SPC

Set the mark, pushing it onto the mark ring, without activating it.

C-u C-SPC

Move point to where the mark was, and restore the mark from the ring
of former marks.

The command C-SPC C-SPC is handy when you want to
use the mark to remember a position to which you may wish to return.
It pushes the current point onto the mark ring, without activating the
mark (which would cause Emacs to highlight the region). This is
actually two consecutive invocations of C-SPC
(set-mark-command); the first C-SPC sets the mark,
and the second C-SPC deactivates it. (When Transient Mark
mode is off, C-SPC C-SPC instead activates Transient
Mark mode temporarily; see Disabled Transient Mark.)

To return to a marked position, use set-mark-command with a
prefix argument: C-u C-SPC. This moves point to where the
mark was, and deactivates the mark if it was active. Each subsequent
C-u C-SPC jumps to a prior position stored in the mark
ring. The positions you move through in this way are not lost; they
go to the end of the ring.

If you set set-mark-command-repeat-pop to non-nil,
then immediately after you type C-u C-SPC, you can type
C-SPC instead of C-u C-SPC to cycle through
the mark ring. By default, set-mark-command-repeat-pop is
nil.

Each buffer has its own mark ring. All editing commands use the
current buffer’s mark ring. In particular, C-u C-SPC
always stays in the same buffer.

The variable mark-ring-max specifies the maximum number of
entries to keep in the mark ring. This defaults to 16 entries. If
that many entries exist and another one is pushed, the earliest one in
the list is discarded. Repeating C-u C-SPC cycles through
the positions currently in the ring.

If you want to move back to the same place over and over, the mark
ring may not be convenient enough. If so, you can record the position
in a register for later retrieval (see Saving
Positions in Registers).

11.5 The Global Mark Ring

In addition to the ordinary mark ring that belongs to each buffer,
Emacs has a single global mark ring. Each time you set a mark,
this is recorded in the global mark ring in addition to the current
buffer’s own mark ring, if you have switched buffers since the
previous mark setting. Hence, the global mark ring records a sequence
of buffers that you have been in, and, for each buffer, a place where
you set the mark. The length of the global mark ring is controlled by
global-mark-ring-max, and is 16 by default.

The command C-x C-SPC (pop-global-mark) jumps to
the buffer and position of the latest entry in the global ring. It also
rotates the ring, so that successive uses of C-x C-SPC take
you to earlier buffers and mark positions.

11.6 Shift Selection

If you hold down the shift key while typing a cursor motion command,
this sets the mark before moving point, so that the region extends
from the original position of point to its new position. This feature
is referred to as shift-selection. It is similar to the way
text is selected in other editors.

The mark set via shift-selection behaves a little differently from
what we have described above. Firstly, in addition to the usual ways
of deactivating the mark (such as changing the buffer text or typing
C-g), the mark is deactivated by any unshifted cursor
motion command. Secondly, any subsequent shifted cursor motion
command avoids setting the mark anew. Therefore, a series of shifted
cursor motion commands will continuously adjust the region.

Shift-selection only works if the shifted cursor motion key is not
already bound to a separate command (see Customization). For
example, if you bind S-C-f to another command, typing
S-C-f runs that command instead of performing a shift-selected
version of C-f (forward-char).

A mark set via mouse commands behaves the same as a mark set via
shift-selection (see Setting Mark). For example, if you specify a
region by dragging the mouse, you can continue to extend the region
using shifted cursor motion commands. In either case, any unshifted
cursor motion command deactivates the mark.

To turn off shift-selection, set shift-select-mode to
nil. Doing so does not disable setting the mark via mouse
commands.

11.7 Disabling Transient Mark Mode

The default behavior of the mark and region, in which setting the
mark activates it and highlights the region, is called Transient Mark
mode. This is a minor mode that is enabled by default. It can be
toggled with M-x transient-mark-mode, or with the ‘Active
Region Highlighting’ menu item in the ‘Options’ menu. Turning it
off switches Emacs to an alternative mode of operation:

Setting the mark, with commands like C-SPC or C-x
C-x, does not highlight the region. Therefore, you can’t tell by
looking where the mark is located; you have to remember.

The usual solution to this problem is to set the mark and then use it
soon, before you forget where it is. You can also check where the
mark is by using C-x C-x, which exchanges the positions of the
point and the mark (see Setting Mark).

Some commands, which ordinarily act on the region when the mark is
active, no longer do so. For example, normally M-%
(query-replace) performs replacements within the region, if the
mark is active. When Transient Mark mode is off, it always operates
from point to the end of the buffer. Commands that act this way are
identified in their own documentation.

While Transient Mark mode is off, you can activate it temporarily
using C-SPC C-SPC or C-u C-x C-x.

C-SPC C-SPC

Set the mark at point (like plain C-SPC) and enable
Transient Mark mode just once, until the mark is deactivated. (This
is not really a separate command; you are using the C-SPC
command twice.)

C-u C-x C-x

Exchange point and mark, activate the mark and enable Transient Mark
mode temporarily, until the mark is next deactivated. (This is the
C-x C-x command, exchange-point-and-mark, with a prefix
argument.)

These commands set or activate the mark, and enable Transient Mark
mode only until the mark is deactivated. One reason you may want to
use them is that some commands operate on the entire buffer instead of
the region when Transient Mark mode is off. Enabling Transient Mark
mode momentarily gives you a way to use these commands on the region.

When you specify a region with the mouse (see Setting Mark), or
with shift-selection (see Shift Selection), this likewise
activates Transient Mark mode temporarily and highlights the region.

12 Killing and Moving Text

In Emacs, killing means erasing text and copying it into the
kill ring. Yanking means bringing text from the kill ring
back into the buffer. (Some applications use the terms “cutting”
and “pasting” for similar operations.) The kill ring is so-named
because it can be visualized as a set of blocks of text arranged in a
ring, which you can access in cyclic order. See Kill Ring.

Killing and yanking are the most common way to move or copy text
within Emacs. It is very versatile, because there are commands for
killing many different types of syntactic units.

12.1 Deletion and Killing

Most commands which erase text from the buffer save it in the kill
ring. These are known as kill commands, and their names
normally contain the word ‘kill’ (e.g., kill-line). The
kill ring stores several recent kills, not just the last one, so
killing is a very safe operation: you don’t have to worry much about
losing text that you previously killed. The kill ring is shared by
all buffers, so text that is killed in one buffer can be yanked into
another buffer.

When you use C-/ (undo) to undo a kill command
(see Undo), that brings the killed text back into the buffer, but
does not remove it from the kill ring.

On graphical displays, killing text also copies it to the system
clipboard. See Cut and Paste.

Commands that erase text but do not save it in the kill ring are
known as delete commands; their names usually contain the word
‘delete’. These include C-d (delete-char) and
DEL (delete-backward-char), which delete only one
character at a time, and those commands that delete only spaces or
newlines. Commands that can erase significant amounts of nontrivial
data generally do a kill operation instead.

12.1.1 Deletion

Deletion means erasing text and not saving it in the kill ring. For
the most part, the Emacs commands that delete text are those that
erase just one character or only whitespace.

DEL

BACKSPACE

Delete the previous character, or the text in the region if it is
active (delete-backward-char).

Delete

Delete the next character, or the text in the region if it is active
(delete-forward-char).

C-d

Delete the next character (delete-char).

M-\

Delete spaces and tabs around point (delete-horizontal-space).

M-SPC

Delete spaces and tabs around point, leaving one space
(just-one-space).

C-x C-o

Delete blank lines around the current line (delete-blank-lines).

M-^

Join two lines by deleting the intervening newline, along with any
indentation following it (delete-indentation).

We have already described the basic deletion commands DEL
(delete-backward-char), delete
(delete-forward-char), and C-d (delete-char).
See Erasing. With a numeric argument, they delete the specified
number of characters. If the numeric argument is omitted or one, they
delete all the text in the region if it is active (see Using Region).

The other delete commands are those that delete only whitespace
characters: spaces, tabs and newlines. M-\
(delete-horizontal-space) deletes all the spaces and tab
characters before and after point. With a prefix argument, this only
deletes spaces and tab characters before point. M-SPC
(just-one-space) does likewise but leaves a single space before
point, regardless of the number of spaces that existed previously
(even if there were none before). With a numeric argument n, it
leaves n spaces before point if n is positive; if n
is negative, it deletes newlines in addition to spaces and tabs,
leaving -n spaces before point. The command cycle-spacing
acts like a more flexible version of just-one-space. It
does different things if you call it repeatedly in succession.
The first call acts like just-one-space, the next removes
all whitespace, and a third call restores the original whitespace.

C-x C-o (delete-blank-lines) deletes all blank lines
after the current line. If the current line is blank, it deletes all
blank lines preceding the current line as well (leaving one blank line,
the current line). On a solitary blank line, it deletes that line.

M-^ (delete-indentation) joins the current line and the
previous line, by deleting a newline and all surrounding spaces, usually
leaving a single space. See M-^.

The command delete-duplicate-lines searches the region for
identical lines, and removes all but one copy of each. Normally it
keeps the first instance of each repeated line, but with a C-u
prefix argument it keeps the last. With a C-u C-u prefix
argument, it only searches for adjacent identical lines. This is a
more efficient mode of operation, useful when the lines have already
been sorted. With a C-u C-u C-u prefix argument, it retains
repeated blank lines.

12.1.2 Killing by Lines

C-k

Kill rest of line or one or more lines (kill-line).

C-S-backspace

Kill an entire line at once (kill-whole-line)

The simplest kill command is C-k (kill-line). If used
at the end of a line, it kills the line-ending newline character,
merging the next line into the current one (thus, a blank line is
entirely removed). Otherwise, C-k kills all the text from point
up to the end of the line; if point was originally at the beginning of
the line, this leaves the line blank.

Spaces and tabs at the end of the line are ignored when deciding
which case applies. As long as point is after the last visible
character in the line, you can be sure that C-k will kill the
newline. To kill an entire non-blank line, go to the beginning and
type C-k twice.

In this context, “line” means a logical text line, not a screen
line (see Continuation Lines).

When C-k is given a positive argument n, it kills
n lines and the newlines that follow them (text on the current
line before point is not killed). With a negative argument
-n, it kills n lines preceding the current line,
together with the text on the current line before point. C-k
with an argument of zero kills the text before point on the current
line.

If the variable kill-whole-line is non-nil, C-k at
the very beginning of a line kills the entire line including the
following newline. This variable is normally nil.

C-S-backspace (kill-whole-line) kills a whole line
including its newline, regardless of the position of point within the
line. Note that many text terminals will prevent you from typing the
key sequence C-S-backspace.

One of the commonly-used kill commands is C-w
(kill-region), which kills the text in the region
(see Mark). Similarly, M-w (kill-ring-save) copies
the text in the region into the kill ring without removing it from the
buffer. If the mark is inactive when you type C-w or M-w,
the command acts on the text between point and where you last set the
mark (see Using Region).

The command M-z (zap-to-char) combines killing with
searching: it reads a character and kills from point up to (and
including) the next occurrence of that character in the buffer. A
numeric argument acts as a repeat count; a negative argument means to
search backward and kill text before point.

12.1.4 Options for Killing

Some specialized buffers contain read-only text, which cannot
be modified and therefore cannot be killed. The kill commands work
specially in a read-only buffer: they move over text and copy it to
the kill ring, without actually deleting it from the buffer.
Normally, they also beep and display an error message when this
happens. But if you set the variable kill-read-only-ok to a
non-nil value, they just print a message in the echo area to
explain why the text has not been erased.

If you change the variable kill-do-not-save-duplicates to a
non-nil value, identical subsequent kills yield a single
kill-ring entry, without duplication.

12.2 Yanking

Yanking means reinserting text previously killed. The usual
way to move or copy text is to kill it and then yank it elsewhere.

C-y

Yank the last kill into the buffer, at point (yank).

M-y

Replace the text just yanked with an earlier batch of killed text
(yank-pop). See Earlier Kills.

C-M-w

Cause the following command, if it is a kill command, to append to the
previous kill (append-next-kill). See Appending Kills.

The basic yanking command is C-y (yank). It inserts
the most recent kill, leaving the cursor at the end of the inserted
text. It also sets the mark at the beginning of the inserted text,
without activating the mark; this lets you jump easily to that
position, if you wish, with C-u C-SPC (see Mark Ring).

With a plain prefix argument (C-u C-y), the command instead
leaves the cursor in front of the inserted text, and sets the mark at
the end. Using any other prefix argument specifies an earlier kill;
e.g., C-u 4 C-y reinserts the fourth most recent kill.
See Earlier Kills.

On graphical displays, C-y first checks if another application
has placed any text in the system clipboard more recently than the
last Emacs kill. If so, it inserts the clipboard’s text instead.
Thus, Emacs effectively treats “cut” or “copy” clipboard
operations performed in other applications like Emacs kills, except
that they are not recorded in the kill ring. See Cut and Paste,
for details.

12.2.1 The Kill Ring

The kill ring is a list of blocks of text that were previously
killed. There is only one kill ring, shared by all buffers, so you
can kill text in one buffer and yank it in another buffer. This is
the usual way to move text from one buffer to another. (There are
several other methods: for instance, you could store the text in a
register; see Registers. See Accumulating Text, for some
other ways to move text around.)

The maximum number of entries in the kill ring is controlled by the
variable kill-ring-max. The default is 60. If you make a new
kill when this limit has been reached, Emacs makes room by deleting
the oldest entry in the kill ring.

The actual contents of the kill ring are stored in a variable named
kill-ring; you can view the entire contents of the kill ring
with C-h v kill-ring.

12.2.2 Yanking Earlier Kills

As explained in Yanking, you can use a numeric argument to
C-y to yank text that is no longer the most recent kill. This
is useful if you remember which kill ring entry you want. If you
don’t, you can use the M-y (yank-pop) command to cycle
through the possibilities.

If the previous command was a yank command, M-y takes the text
that was yanked and replaces it with the text from an earlier kill.
So, to recover the text of the next-to-the-last kill, first use
C-y to yank the last kill, and then use M-y to replace it
with the previous kill. M-y is allowed only after a C-y
or another M-y.

You can understand M-y in terms of a “last yank” pointer which
points at an entry in the kill ring. Each time you kill, the “last
yank” pointer moves to the newly made entry at the front of the ring.
C-y yanks the entry which the “last yank” pointer points to.
M-y moves the “last yank” pointer to a different entry, and the
text in the buffer changes to match. Enough M-y commands can move
the pointer to any entry in the ring, so you can get any entry into the
buffer. Eventually the pointer reaches the end of the ring; the next
M-y loops back around to the first entry again.

M-y moves the “last yank” pointer around the ring, but it does
not change the order of the entries in the ring, which always runs from
the most recent kill at the front to the oldest one still remembered.

M-y can take a numeric argument, which tells it how many entries
to advance the “last yank” pointer by. A negative argument moves the
pointer toward the front of the ring; from the front of the ring, it
moves “around” to the last entry and continues forward from there.

Once the text you are looking for is brought into the buffer, you can
stop doing M-y commands and it will stay there. It’s just a copy
of the kill ring entry, so editing it in the buffer does not change
what’s in the ring. As long as no new killing is done, the “last
yank” pointer remains at the same place in the kill ring, so repeating
C-y will yank another copy of the same previous kill.

When you call C-y with a numeric argument, that also sets the
“last yank” pointer to the entry that it yanks.

12.2.3 Appending Kills

Normally, each kill command pushes a new entry onto the kill ring.
However, two or more kill commands in a row combine their text into a
single entry, so that a single C-y yanks all the text as a unit,
just as it was before it was killed.

Thus, if you want to yank text as a unit, you need not kill all of it
with one command; you can keep killing line after line, or word after
word, until you have killed it all, and you can still get it all back at
once.

Commands that kill forward from point add onto the end of the previous
killed text. Commands that kill backward from point add text onto the
beginning. This way, any sequence of mixed forward and backward kill
commands puts all the killed text into one entry without rearrangement.
Numeric arguments do not break the sequence of appending kills. For
example, suppose the buffer contains this text:

This is a line ∗of sample text.

with point shown by ∗. If you type M-d M-DEL M-d
M-DEL, killing alternately forward and backward, you end up with
‘a line of sample’ as one entry in the kill ring, and ‘This
is text.’ in the buffer. (Note the double space between ‘is’
and ‘text’, which you can clean up with M-SPC or
M-q.)

Another way to kill the same text is to move back two words with
M-b M-b, then kill all four words forward with C-u M-d.
This produces exactly the same results in the buffer and in the kill
ring. M-f M-f C-u M-DEL kills the same text, all going
backward; once again, the result is the same. The text in the kill ring
entry always has the same order that it had in the buffer before you
killed it.

If a kill command is separated from the last kill command by other
commands (not just numeric arguments), it starts a new entry on the
kill ring. But you can force it to combine with the last killed text,
by typing C-M-w (append-next-kill) right beforehand. The
C-M-w tells its following command, if it is a kill command, to
treat the kill as part of the sequence of previous kills. As usual,
the kill is appended to the previous killed text if the command kills
forward, and prepended if the command kills backward. In this way,
you can kill several separated pieces of text and accumulate them to
be yanked back in one place.

A kill command following M-w (kill-ring-save) does not
append to the text that M-w copied into the kill ring.

12.3 “Cut and Paste” Operations on Graphical Displays

In most graphical desktop environments, you can transfer data
(usually text) between different applications using a system facility
called the clipboard. On X, two other similar facilities are
available: the primary selection and the secondary selection. When
Emacs is run on a graphical display, its kill and yank commands
integrate with these facilities, so that you can easily transfer text
between Emacs and other graphical applications.

By default, Emacs uses UTF-8 as the coding system for inter-program
text transfers. If you find that the pasted text is not what you
expected, you can specify another coding system by typing C-x
RET x or C-x RET X. You can also request a
different data type by customizing x-select-request-type.
See Communication Coding.

12.3.1 Using the Clipboard

The clipboard is the facility that most graphical applications
use for “cutting and pasting”. When the clipboard exists, the kill
and yank commands in Emacs make use of it.

When you kill some text with a command such as C-w
(kill-region), or copy it to the kill ring with a command such
as M-w (kill-ring-save), that text is also put in the
clipboard.

When an Emacs kill command puts text in the clipboard, the existing
clipboard contents are normally lost. Optionally, you can change
save-interprogram-paste-before-kill to t. Then Emacs
will first save the clipboard to its kill ring, preventing you from
losing the old clipboard data—at the risk of high memory consumption
if that data turns out to be large.

Yank commands, such as C-y (yank), also use the
clipboard. If another application “owns” the clipboard—i.e., if
you cut or copied text there more recently than your last kill command
in Emacs—then Emacs yanks from the clipboard instead of the kill
ring.

Normally, rotating the kill ring with M-y (yank-pop)
does not alter the clipboard. However, if you change
yank-pop-change-selection to t, then M-y saves the
new yank to the clipboard.

To prevent kill and yank commands from accessing the clipboard,
change the variable x-select-enable-clipboard to nil.

Many X desktop environments support a feature called the
clipboard manager. If you exit Emacs while it is the current
“owner” of the clipboard data, and there is a clipboard manager
running, Emacs transfers the clipboard data to the clipboard manager
so that it is not lost. In some circumstances, this may cause a delay
when exiting Emacs; if you wish to prevent Emacs from transferring
data to the clipboard manager, change the variable
x-select-enable-clipboard-manager to nil.

Prior to Emacs 24, the kill and yank commands used the primary
selection (see Primary Selection), not the clipboard. If you
prefer this behavior, change x-select-enable-clipboard to
nil, x-select-enable-primary to t, and
mouse-drag-copy-region to t. In this case, you can use
the following commands to act explicitly on the clipboard:
clipboard-kill-region kills the region and saves it to the
clipboard; clipboard-kill-ring-save copies the region to the
kill ring and saves it to the clipboard; and clipboard-yank
yanks the contents of the clipboard at point.

12.3.2 Cut and Paste with Other Window Applications

Under the X Window System, there exists a primary selection
containing the last stretch of text selected in an X application
(usually by dragging the mouse). Typically, this text can be inserted
into other X applications by mouse-2 clicks. The primary
selection is separate from the clipboard. Its contents are more
“fragile”; they are overwritten each time you select text with the
mouse, whereas the clipboard is only overwritten by explicit “cut”
or “copy” commands.

Under X, whenever the region is active (see Mark), the text in
the region is saved in the primary selection. This applies regardless
of whether the region was made by dragging or clicking the mouse
(see Mouse Commands), or by keyboard commands (e.g., by typing
C-SPC and moving point; see Setting Mark).

If you change the variable select-active-regions to
only, Emacs saves only temporarily active regions to the
primary selection, i.e., those made with the mouse or with shift
selection (see Shift Selection). If you change
select-active-regions to nil, Emacs avoids saving active
regions to the primary selection entirely.

To insert the primary selection into an Emacs buffer, click
mouse-2 (mouse-yank-primary) where you want to insert it.
See Mouse Commands.

MS-Windows provides no primary selection, but Emacs emulates it
within a single Emacs session by storing the selected text internally.
Therefore, all the features and commands related to the primary
selection work on Windows as they do on X, for cutting and pasting
within the same session, but not across Emacs sessions or with other
applications.

12.3.3 Secondary Selection

In addition to the primary selection, the X Window System provides a
second similar facility known as the secondary selection.
Nowadays, few X applications make use of the secondary selection, but
you can access it using the following Emacs commands:

M-Drag-Mouse-1

Set the secondary selection, with one end at the place where you press
down the button, and the other end at the place where you release it
(mouse-set-secondary). The selected text is highlighted, using
the secondary-selection face, as you drag. The window scrolls
automatically if you drag the mouse off the top or bottom of the
window, just like mouse-set-region (see Mouse Commands).

This command does not alter the kill ring.

M-Mouse-1

Set one endpoint for the secondary selection
(mouse-start-secondary).

M-Mouse-3

Set the secondary selection, with one end at the position clicked and
the other at the position specified with M-Mouse-1
(mouse-secondary-save-then-kill). This also puts the selected
text in the kill ring. A second M-Mouse-3 at the same place
kills the secondary selection just made.

M-Mouse-2

Insert the secondary selection where you click, placing point at the
end of the yanked text (mouse-yank-secondary).

Double or triple clicking of M-Mouse-1 operates on words and
lines, much like Mouse-1.

If mouse-yank-at-point is non-nil, M-Mouse-2 yanks
at point. Then it does not matter precisely where you click, or even
which of the frame’s windows you click on. See Mouse Commands.

12.4 Accumulating Text

Usually we copy or move text by killing it and yanking it, but there
are other convenient methods for copying one block of text in many
places, or for copying many scattered blocks of text into one place.
Here we describe the commands to accumulate scattered pieces of text
into a buffer or into a file.

M-x append-to-buffer

Append region to the contents of a specified buffer.

M-x prepend-to-buffer

Prepend region to the contents of a specified buffer.

M-x copy-to-buffer

Copy region into a specified buffer, deleting that buffer’s old contents.

M-x insert-buffer

Insert the contents of a specified buffer into current buffer at point.

M-x append-to-file

Append region to the contents of a specified file, at the end.

To accumulate text into a buffer, use M-x append-to-buffer.
This reads a buffer name, then inserts a copy of the region into the
buffer specified. If you specify a nonexistent buffer,
append-to-buffer creates the buffer. The text is inserted
wherever point is in that buffer. If you have been using the buffer for
editing, the copied text goes into the middle of the text of the buffer,
starting from wherever point happens to be at that moment.

Point in that buffer is left at the end of the copied text, so
successive uses of append-to-buffer accumulate the text in the
specified buffer in the same order as they were copied. Strictly
speaking, append-to-buffer does not always append to the text
already in the buffer—it appends only if point in that buffer is at
the end. However, if append-to-buffer is the only command you
use to alter a buffer, then point is always at the end.

M-x prepend-to-buffer is just like append-to-buffer
except that point in the other buffer is left before the copied text, so
successive prependings add text in reverse order. M-x
copy-to-buffer is similar, except that any existing text in the other
buffer is deleted, so the buffer is left containing just the text newly
copied into it.

The command M-x insert-buffer can be used to retrieve the
accumulated text from another buffer. This prompts for the name of a
buffer, and inserts a copy of all the text in that buffer into the
current buffer at point, leaving point at the beginning of the
inserted text. It also adds the position of the end of the inserted
text to the mark ring, without activating the mark. See Buffers,
for background information on buffers.

Instead of accumulating text in a buffer, you can append text
directly into a file with M-x append-to-file. This prompts for
a filename, and adds the text of the region to the end of the
specified file. The file is changed immediately on disk.

You should use append-to-file only with files that are
not being visited in Emacs. Using it on a file that you are
editing in Emacs would change the file behind Emacs’s back, which
can lead to losing some of your editing.

Another way to move text around is to store it in a register.
See Registers.

12.5 Rectangles

Rectangle commands operate on rectangular areas of the text:
all the characters between a certain pair of columns, in a certain
range of lines. Emacs has commands to kill rectangles, yank killed
rectangles, clear them out, fill them with blanks or text, or delete
them. Rectangle commands are useful with text in multicolumn formats,
and for changing text into or out of such formats.

To specify a rectangle for a command to work on, set the mark at one
corner and point at the opposite corner. The rectangle thus specified
is called the region-rectangle. If point and the mark are in
the same column, the region-rectangle is empty. If they are in the
same line, the region-rectangle is one line high.

The region-rectangle is controlled in much the same way as the
region is controlled. But remember that a given combination of point
and mark values can be interpreted either as a region or as a
rectangle, depending on the command that uses them.

C-x r k

Kill the text of the region-rectangle, saving its contents as the
“last killed rectangle” (kill-rectangle).

C-x r M-w

Save the text of the region-rectangle as the “last killed rectangle”
(copy-rectangle-as-kill).

C-x r d

Delete the text of the region-rectangle (delete-rectangle).

C-x r y

Yank the last killed rectangle with its upper left corner at point
(yank-rectangle).

C-x r o

Insert blank space to fill the space of the region-rectangle
(open-rectangle). This pushes the previous contents of the
region-rectangle to the right.

C-x r N

Insert line numbers along the left edge of the region-rectangle
(rectangle-number-lines). This pushes the previous contents of
the region-rectangle to the right.

C-x r c

Clear the region-rectangle by replacing all of its contents with spaces
(clear-rectangle).

M-x delete-whitespace-rectangle

Delete whitespace in each of the lines on the specified rectangle,
starting from the left edge column of the rectangle.

C-x r t stringRET

Replace rectangle contents with string on each line
(string-rectangle).

M-x string-insert-rectangle RETstringRET

Insert string on each line of the rectangle.

C-x SPC

Toggle Rectangle Mark mode (rectangle-mark-mode).
When this mode is active, the region-rectangle is highlighted and can
be shrunk/grown, and the standard kill and yank commands operate on it.

The rectangle operations fall into two classes: commands to erase or
insert rectangles, and commands to make blank rectangles.

There are two ways to erase the text in a rectangle: C-x r d
(delete-rectangle) to delete the text outright, or C-x r
k (kill-rectangle) to remove the text and save it as the
last killed rectangle. In both cases, erasing the
region-rectangle is like erasing the specified text on each line of
the rectangle; if there is any following text on the line, it moves
backwards to fill the gap.

“Killing” a rectangle is not killing in the usual sense; the
rectangle is not stored in the kill ring, but in a special place that
only records the most recent rectangle killed. This is because
yanking a rectangle is so different from yanking linear text that
different yank commands have to be used. Yank-popping is not defined
for rectangles.

C-x r M-w (copy-rectangle-as-kill) is the equivalent of
M-w for rectangles: it records the rectangle as the “last
killed rectangle”, without deleting the text from the buffer.

To yank the last killed rectangle, type C-x r y
(yank-rectangle). The rectangle’s first line is inserted at
point, the rectangle’s second line is inserted at the same horizontal
position one line vertically below, and so on. The number of lines
affected is determined by the height of the saved rectangle.

For example, you can convert two single-column lists into a
double-column list by killing one of the single-column lists as a
rectangle, and then yanking it beside the other list.

You can also copy rectangles into and out of registers with C-x r
r r and C-x r i r. See Rectangle Registers.

There are two commands you can use for making blank rectangles:
C-x r c (clear-rectangle) blanks out existing text in the
region-rectangle, and C-x r o (open-rectangle) inserts a
blank rectangle.

M-x delete-whitespace-rectangle deletes horizontal whitespace
starting from a particular column. This applies to each of the lines
in the rectangle, and the column is specified by the left edge of the
rectangle. The right edge of the rectangle does not make any
difference to this command.

The command C-x r N (rectangle-number-lines) inserts
line numbers along the left edge of the region-rectangle. Normally,
the numbering begins from 1 (for the first line of the rectangle).
With a prefix argument, the command prompts for a number to begin
from, and for a format string with which to print the numbers
(see Formatting Strings in The Emacs Lisp Reference
Manual).

The command C-x r t (string-rectangle) replaces the
contents of a region-rectangle with a string on each line. The
string’s width need not be the same as the width of the rectangle. If
the string’s width is less, the text after the rectangle shifts left;
if the string is wider than the rectangle, the text after the
rectangle shifts right.

The command M-x string-insert-rectangle is similar to
string-rectangle, but inserts the string on each line,
shifting the original text to the right.

The command C-x SPC (rectangle-mark-mode) toggles
whether the region-rectangle or the standard region is highlighted
(first activating the region if necessary). When this mode is enabled,
commands that resize the region (C-f, C-n etc.) do
so in a rectangular fashion, and killing and yanking operate on the
rectangle. See Killing. The mode persists only as long as the
region is active.

12.6 CUA Bindings

The command M-x cua-mode sets up key bindings that are
compatible with the Common User Access (CUA) system used in many other
applications.

When CUA mode is enabled, the keys C-x, C-c, C-v,
and C-z invoke commands that cut (kill), copy, paste (yank), and
undo respectively. The C-x and C-c keys perform cut and
copy only if the region is active. Otherwise, they still act as
prefix keys, so that standard Emacs commands like C-x C-c still
work. Note that this means the variable mark-even-if-inactive
has no effect for C-x and C-c (see Using Region).

To enter an Emacs command like C-x C-f while the mark is
active, use one of the following methods: either hold Shift
together with the prefix key, e.g., S-C-x C-f, or quickly type
the prefix key twice, e.g., C-x C-x C-f.

To disable the overriding of standard Emacs binding by CUA mode,
while retaining the other features of CUA mode described below, set
the variable cua-enable-cua-keys to nil.

CUA mode by default activates Delete-Selection mode (see Mouse Commands)
so that typed text replaces the active region. To use CUA without this
behavior, set the variable cua-delete-selection to nil.

CUA mode provides enhanced rectangle support with visible
rectangle highlighting. Use C-RET to start a rectangle,
extend it using the movement commands, and cut or copy it using
C-x or C-c. RET moves the cursor to the next
(clockwise) corner of the rectangle, so you can easily expand it in
any direction. Normal text you type is inserted to the left or right
of each line in the rectangle (on the same side as the cursor).

You can use this rectangle support without activating CUA by calling the
cua-rectangle-mark-mode command. But see also the standard
rectangle-mark-mode. See Rectangles.

With CUA you can easily copy text and rectangles into and out of
registers by providing a one-digit numeric prefix to the kill, copy,
and yank commands, e.g., C-1 C-c copies the region into register
1, and C-2 C-v yanks the contents of register 2.

CUA mode also has a global mark feature which allows easy moving and
copying of text between buffers. Use C-S-SPC to toggle the
global mark on and off. When the global mark is on, all text that you
kill or copy is automatically inserted at the global mark, and text
you type is inserted at the global mark rather than at the current
position.

For example, to copy words from various buffers into a word list in
a given buffer, set the global mark in the target buffer, then
navigate to each of the words you want in the list, mark it (e.g., with
S-M-f), copy it to the list with C-c or M-w, and
insert a newline after the word in the target list by pressing
RET.

13 Registers

Emacs registers are compartments where you can save text,
rectangles, positions, and other things for later use. Once you save
text or a rectangle in a register, you can copy it into the buffer
once, or many times; once you save a position in a register, you can
jump back to that position once, or many times.

Each register has a name that consists of a single character, which
we will denote by r; r can be a letter (such as ‘a’)
or a number (such as ‘1’); case matters, so register ‘a’ is
not the same as register ‘A’.

A register can store a position, a piece of text, a rectangle, a
number, a window configuration, or a file name, but only one thing at
any given time. Whatever you store in a register remains there until
you store something else in that register. To see what register
r contains, use M-x view-register:

M-x view-register RETr

Display a description of what register r contains.

All of the commands that prompt for a register will display a
“preview” window that lists the existing registers (if there are
any) after a short delay. To change the length of the delay,
customize register-preview-delay. To prevent this display, set
that option to nil. You can explicitly request a preview
window by pressing C-h or F1.

Bookmarks record files and positions in them, so you can
return to those positions when you look at the file again. Bookmarks
are similar in spirit to registers, so they are also documented in
this chapter.

13.1 Saving Positions in Registers

C-x r SPCr

Record the position of point and the current buffer in register
r (point-to-register).

C-x r j r

Jump to the position and buffer saved in register r
(jump-to-register).

Typing C-x r SPC (point-to-register), followed by
a character r, saves both the position of point and the
current buffer in register r. The register retains this
information until you store something else in it.

The command C-x r j r switches to the buffer recorded in
register r, and moves point to the recorded position. The
contents of the register are not changed, so you can jump to the saved
position any number of times.

If you use C-x r j to go to a saved position, but the buffer it
was saved from has been killed, C-x r j tries to create the buffer
again by visiting the same file. Of course, this works only for buffers
that were visiting files.

13.2 Saving Text in Registers

When you want to insert a copy of the same piece of text several
times, it may be inconvenient to yank it from the kill ring, since each
subsequent kill moves that entry further down the ring. An alternative
is to store the text in a register and later retrieve it.

C-x r s r

Copy region into register r (copy-to-register).

C-x r i r

Insert text from register r (insert-register).

M-x append-to-register RETr

Append region to text in register r.

When register r contains text, you can use C-x r +
(increment-register) to append to that register. Note that
command C-x r + behaves differently if r contains a
number. See Number Registers.

M-x prepend-to-register RETr

Prepend region to text in register r.

C-x r s r stores a copy of the text of the region into
the register named r. If the mark is inactive, Emacs first
reactivates the mark where it was last set. The mark is deactivated
at the end of this command. See Mark. C-u C-x r s r,
the same command with a prefix argument, copies the text into register
r and deletes the text from the buffer as well; you can think of
this as “moving” the region text into the register.

M-x append-to-register RETr appends the copy of
the text in the region to the text already stored in the register
named r. If invoked with a prefix argument, it deletes the
region after appending it to the register. The command
prepend-to-register is similar, except that it prepends
the region text to the text in the register instead of
appending it.

When you are collecting text using append-to-register and
prepend-to-register, you may want to separate individual
collected pieces using a separator. In that case, configure a
register-separator and store the separator text in to that
register. For example, to get double newlines as text separator
during the collection process, you can use the following setting.

(setq register-separator ?+)
(set-register register-separator "\n\n")

C-x r i r inserts in the buffer the text from register
r. Normally it leaves point before the text and sets the mark
after, without activating it. With a numeric argument, it instead
puts point after the text and the mark before.

13.4 Saving Window Configurations in Registers

You can save the window configuration of the selected frame in a
register, or even the configuration of all windows in all frames, and
restore the configuration later. See Windows, for information
about window configurations.

C-x r w r

Save the state of the selected frame’s windows in register r
(window-configuration-to-register).

C-x r f r

Save the state of all frames, including all their windows, in register
r (frameset-to-register).

Use C-x r j r to restore a window or frame configuration.
This is the same command used to restore a cursor position. When you
restore a frame configuration, any existing frames not included in the
configuration become invisible. If you wish to delete these frames
instead, use C-u C-x r j r.

13.5 Keeping Numbers in Registers

There are commands to store a number in a register, to insert
the number in the buffer in decimal, and to increment it. These commands
can be useful in keyboard macros (see Keyboard Macros).

C-u number C-x r n r

Store number into register r (number-to-register).

C-u number C-x r + r

If r contains a number, increment the number in that register by
number. Note that command C-x r +
(increment-register) behaves differently if r contains
text. See Text Registers.

C-x r i r

Insert the number from register r into the buffer.

C-x r i is the same command used to insert any other sort of
register contents into the buffer. C-x r + with no numeric
argument increments the register value by 1; C-x r n with no
numeric argument stores zero in the register.

13.7 Keyboard Macro Registers

If you need to execute a keyboard macro (see Keyboard Macros)
frequently, it is more convenient to put it in a register or save it
(see Save Keyboard Macro). C-x C-k x r
(kmacro-to-register) stores the last keyboard macro in register
r.

To execute the keyboard macro in register r, type C-x r j
r. (This is the same command used to jump to a position or
restore a frameset.)

13.8 Bookmarks

Bookmarks are somewhat like registers in that they record
positions you can jump to. Unlike registers, they have long names, and
they persist automatically from one Emacs session to the next. The
prototypical use of bookmarks is to record “where you were reading” in
various files.

C-x r m RET

Set the bookmark for the visited file, at point.

C-x r m bookmarkRET

Set the bookmark named bookmark at point (bookmark-set).

C-x r b bookmarkRET

Jump to the bookmark named bookmark (bookmark-jump).

C-x r l

List all bookmarks (list-bookmarks).

M-x bookmark-save

Save all the current bookmark values in the default bookmark file.

The prototypical use for bookmarks is to record one current position
in each of several files. So the command C-x r m, which sets a
bookmark, uses the visited file name as the default for the bookmark
name. If you name each bookmark after the file it points to, then you
can conveniently revisit any of those files with C-x r b, and move
to the position of the bookmark at the same time.

To display a list of all your bookmarks in a separate buffer, type
C-x r l (list-bookmarks). If you switch to that buffer,
you can use it to edit your bookmark definitions or annotate the
bookmarks. Type C-h m in the bookmark buffer for more
information about its special editing commands.

When you kill Emacs, Emacs saves your bookmarks, if
you have changed any bookmark values. You can also save the bookmarks
at any time with the M-x bookmark-save command. Bookmarks are
saved to the file ~/.emacs.d/bookmarks (for compatibility with
older versions of Emacs, if you have a file named ~/.emacs.bmk,
that is used instead). The bookmark commands load your default
bookmark file automatically. This saving and loading is how bookmarks
persist from one Emacs session to the next.

If you set the variable bookmark-save-flag to 1, each command
that sets a bookmark will also save your bookmarks; this way, you
don’t lose any bookmark values even if Emacs crashes. The value, if
a number, says how many bookmark modifications should go by between
saving. If you set this variable to nil, Emacs only
saves bookmarks if you explicitly use M-x bookmark-save.

The variable bookmark-default-file specifies the file in
which to save bookmarks by default.

Bookmark position values are saved with surrounding context, so that
bookmark-jump can find the proper position even if the file is
modified slightly. The variable bookmark-search-size says how
many characters of context to record on each side of the bookmark’s
position.

Here are some additional commands for working with bookmarks:

M-x bookmark-load RETfilenameRET

Load a file named filename that contains a list of bookmark
values. You can use this command, as well as bookmark-write, to
work with other files of bookmark values in addition to your default
bookmark file.

M-x bookmark-write RETfilenameRET

Save all the current bookmark values in the file filename.

M-x bookmark-delete RETbookmarkRET

Delete the bookmark named bookmark.

M-x bookmark-insert-location RETbookmarkRET

Insert in the buffer the name of the file that bookmark bookmark
points to.

M-x bookmark-insert RETbookmarkRET

Insert in the buffer the contents of the file that bookmark
bookmark points to.

14 Controlling the Display

Since only part of a large buffer fits in the window, Emacs has to
show only a part of it. This chapter describes commands and variables
that let you specify which part of the text you want to see, and how
the text is displayed.

14.1 Scrolling

If a window is too small to display all the text in its buffer, it
displays only a portion of it. Scrolling commands change which
portion of the buffer is displayed.

Scrolling “forward” or “up” advances the portion of the buffer
displayed in the window; equivalently, it moves the buffer text
upwards relative to the window. Scrolling “backward” or “down”
displays an earlier portion of the buffer, and moves the text
downwards relative to the window.

In Emacs, scrolling “up” or “down” refers to the direction that
the text moves in the window, not the direction that the window
moves relative to the text. This terminology was adopted by Emacs
before the modern meaning of “scrolling up” and “scrolling down”
became widespread. Hence, the strange result that PageDown
scrolls “up” in the Emacs sense.

The portion of a buffer displayed in a window always contains point.
If you move point past the bottom or top of the window, scrolling
occurs automatically to bring it back onscreen (see Auto Scrolling). You can also scroll explicitly with these commands:

C-v

next

PageDown

Scroll forward by nearly a full window (scroll-up-command).

M-v

prior

PageUp

Scroll backward (scroll-down-command).

C-v (scroll-up-command) scrolls forward by nearly the
whole window height. The effect is to take the two lines at the
bottom of the window and put them at the top, followed by lines that
were not previously visible. If point was in the text that scrolled
off the top, it ends up on the window’s new topmost line. The
next (or PageDown) key is equivalent to C-v.

M-v (scroll-down-command) scrolls backward in a similar
way. The prior (or PageUp) key is equivalent to
M-v.

The number of lines of overlap left by these scroll commands is
controlled by the variable next-screen-context-lines, whose
default value is 2. You can supply the commands with a numeric prefix
argument, n, to scroll by n lines; Emacs attempts to leave
point unchanged, so that the text and point move up or down together.
C-v with a negative argument is like M-v and vice versa.

By default, these commands signal an error (by beeping or flashing
the screen) if no more scrolling is possible, because the window has
reached the beginning or end of the buffer. If you change the
variable scroll-error-top-bottom to t, the command moves
point to the farthest possible position. If point is already there,
the command signals an error.

Some users like scroll commands to keep point at the same screen
position, so that scrolling back to the same screen conveniently
returns point to its original position. You can enable this behavior
via the variable scroll-preserve-screen-position. If the value
is t, Emacs adjusts point to keep the cursor at the same screen
position whenever a scroll command moves it off-window, rather than
moving it to the topmost or bottommost line. With any other
non-nil value, Emacs adjusts point this way even if the scroll
command leaves point in the window. This variable affects all the
scroll commands documented in this section, as well as scrolling with
the mouse wheel (see Mouse Commands); in general, it affects any
command that has a non-nilscroll-command property.
See Property Lists in The Emacs Lisp Reference Manual.

The commands M-x scroll-up and M-x scroll-down behave
similarly to scroll-up-command and scroll-down-command,
except they do not obey scroll-error-top-bottom. Prior to
Emacs 24, these were the default commands for scrolling up and down.
The commands M-x scroll-up-line and M-x scroll-down-line
scroll the current window by one line at a time. If you intend to use
any of these commands, you might want to give them key bindings
(see Init Rebinding).

14.2 Recentering

C-l

Scroll the selected window so the current line is the center-most text
line; on subsequent consecutive invocations, make the current line the
top line, the bottom line, and so on in cyclic order. Possibly
redisplay the screen too (recenter-top-bottom).

M-x recenter

Scroll the selected window so the current line is the center-most text
line. Possibly redisplay the screen too.

The C-l (recenter-top-bottom) command recenters
the selected window, scrolling it so that the current screen line is
exactly in the center of the window, or as close to the center as
possible.

Typing C-l twice in a row (C-l C-l) scrolls the window
so that point is on the topmost screen line. Typing a third C-l
scrolls the window so that point is on the bottom-most screen line.
Each successive C-l cycles through these three positions.

You can change the cycling order by customizing the list variable
recenter-positions. Each list element should be the symbol
top, middle, or bottom, or a number; an integer
means to move the line to the specified screen line, while a
floating-point number between 0.0 and 1.0 specifies a percentage of
the screen space from the top of the window. The default,
(middle top bottom), is the cycling order described above.
Furthermore, if you change the variable scroll-margin to a
non-zero value n, C-l always leaves at least n
screen lines between point and the top or bottom of the window
(see Auto Scrolling).

You can also give C-l a prefix argument. A plain prefix
argument, C-u C-l, simply recenters point. A positive argument
n puts point n lines down from the top of the window. An
argument of zero puts point on the topmost line. A negative argument
-n puts point n lines from the bottom of the window. When
given an argument, C-l does not clear the screen or cycle
through different screen positions.

If the variable recenter-redisplay has a non-nil
value, each invocation of C-l also clears and redisplays the
screen; the special value tty (the default) says to do this on
text-terminal frames only. Redisplaying is useful in case the screen
becomes garbled for any reason (see Screen Garbled).

The more primitive command M-x recenter behaves like
recenter-top-bottom, but does not cycle among screen positions.

C-M-l (reposition-window) scrolls the current window
heuristically in a way designed to get useful information onto the
screen. For example, in a Lisp file, this command tries to get the
entire current defun onto the screen if possible.

14.3 Automatic Scrolling

Emacs performs automatic scrolling when point moves out of the
visible portion of the text. Normally, automatic scrolling centers
point vertically in the window, but there are several ways to alter
this behavior.

If you set scroll-conservatively to a small number n,
then moving point just a little off the screen (no more than n
lines) causes Emacs to scroll just enough to bring point back on
screen; if doing so fails to make point visible, Emacs scrolls just
far enough to center point in the window. If you set
scroll-conservatively to a large number (larger than 100),
automatic scrolling never centers point, no matter how far point
moves; Emacs always scrolls text just enough to bring point into view,
either at the top or bottom of the window depending on the scroll
direction. By default, scroll-conservatively is 0, which
means to always center point in the window.

Another way to control automatic scrolling is to customize the
variable scroll-step. Its value determines the number of lines
by which to automatically scroll, when point moves off the screen. If
scrolling by that number of lines fails to bring point back into view,
point is centered instead. The default value is zero, which (by
default) causes point to always be centered after scrolling.

A third way to control automatic scrolling is to customize the
variables scroll-up-aggressively and
scroll-down-aggressively, which directly specify the vertical
position of point after scrolling. The value of
scroll-up-aggressively should be either nil (the
default), or a floating point number f between 0 and 1. The
latter means that when point goes below the bottom window edge (i.e.,
scrolling forward), Emacs scrolls the window so that point is f
parts of the window height from the bottom window edge. Thus, larger
f means more aggressive scrolling: more new text is brought into
view. The default value, nil, is equivalent to 0.5.

Likewise, scroll-down-aggressively is used when point goes
above the bottom window edge (i.e., scrolling backward). The value
specifies how far point should be from the top margin of the window
after scrolling. Thus, as with scroll-up-aggressively, a
larger value is more aggressive.

Note that the variables scroll-conservatively,
scroll-step, and scroll-up-aggressively /
scroll-down-aggressively control automatic scrolling in
contradictory ways. Therefore, you should pick no more than one of
these methods to customize automatic scrolling. In case you customize
multiple variables, the order of priority is:
scroll-conservatively, then scroll-step, and finally
scroll-up-aggressively / scroll-down-aggressively.

The variable scroll-margin restricts how close point can come
to the top or bottom of a window (even if aggressive scrolling
specifies a fraction f that is larger than the window portion
between the top and the bottom margins). Its value is a number of screen
lines; if point comes within that many lines of the top or bottom of
the window, Emacs performs automatic scrolling. By default,
scroll-margin is 0.

14.4 Horizontal Scrolling

Horizontal scrolling means shifting all the lines sideways
within a window, so that some of the text near the left margin is not
displayed. When the text in a window is scrolled horizontally, text
lines are truncated rather than continued (see Line Truncation).
If a window shows truncated lines, Emacs performs automatic horizontal
scrolling whenever point moves off the left or right edge of the
screen. To disable automatic horizontal scrolling, set the variable
auto-hscroll-mode to nil. Note that when the automatic
horizontal scrolling is turned off, if point moves off the edge of the
screen, the cursor disappears to indicate that. (On text terminals,
the cursor is left at the edge instead.)

The variable hscroll-margin controls how close point can get
to the window’s left and right edges before automatic scrolling
occurs. It is measured in columns. For example, if the value is 5,
then moving point within 5 columns of an edge causes horizontal
scrolling away from that edge.

The variable hscroll-step determines how many columns to
scroll the window when point gets too close to the edge. Zero, the
default value, means to center point horizontally within the window.
A positive integer value specifies the number of columns to scroll by.
A floating-point number specifies the fraction of the window’s width
to scroll by.

You can also perform explicit horizontal scrolling with the
following commands:

C-x <

Scroll text in current window to the left (scroll-left).

C-x >

Scroll to the right (scroll-right).

C-x < (scroll-left) scrolls text in the selected window
to the left by the full width of the window, less two columns. (In
other words, the text in the window moves left relative to the
window.) With a numeric argument n, it scrolls by n
columns.

If the text is scrolled to the left, and point moves off the left
edge of the window, the cursor will freeze at the left edge of the
window, until point moves back to the displayed portion of the text.
This is independent of the current setting of
auto-hscroll-mode, which, for text scrolled to the left, only
affects the behavior at the right edge of the window.

C-x > (scroll-right) scrolls similarly to the right.
The window cannot be scrolled any farther to the right once it is
displayed normally, with each line starting at the window’s left
margin; attempting to do so has no effect. This means that you don’t
have to calculate the argument precisely for C-x >; any
sufficiently large argument will restore the normal display.

If you use those commands to scroll a window horizontally, that sets
a lower bound for automatic horizontal scrolling. Automatic scrolling
will continue to scroll the window, but never farther to the right
than the amount you previously set by scroll-left.

14.5 Narrowing

Narrowing means focusing in on some portion of the buffer,
making the rest temporarily inaccessible. The portion which you can
still get to is called the accessible portion. Canceling the
narrowing, which makes the entire buffer once again accessible, is
called widening. The bounds of narrowing in effect in a buffer
are called the buffer’s restriction.

Narrowing can make it easier to concentrate on a single subroutine or
paragraph by eliminating clutter. It can also be used to limit the
range of operation of a replace command or repeating keyboard macro.

C-x n n

Narrow down to between point and mark (narrow-to-region).

C-x n w

Widen to make the entire buffer accessible again (widen).

C-x n p

Narrow down to the current page (narrow-to-page).

C-x n d

Narrow down to the current defun (narrow-to-defun).

When you have narrowed down to a part of the buffer, that part appears
to be all there is. You can’t see the rest, you can’t move into it
(motion commands won’t go outside the accessible part), you can’t change
it in any way. However, it is not gone, and if you save the file all
the inaccessible text will be saved. The word ‘Narrow’ appears in
the mode line whenever narrowing is in effect.

The primary narrowing command is C-x n n (narrow-to-region).
It sets the current buffer’s restrictions so that the text in the current
region remains accessible, but all text before the region or after the
region is inaccessible. Point and mark do not change.

Alternatively, use C-x n p (narrow-to-page) to narrow
down to the current page. See Pages, for the definition of a page.
C-x n d (narrow-to-defun) narrows down to the defun
containing point (see Defuns).

The way to cancel narrowing is to widen with C-x n w
(widen). This makes all text in the buffer accessible again.

You can get information on what part of the buffer you are narrowed down
to using the C-x = command. See Position Info.

Because narrowing can easily confuse users who do not understand it,
narrow-to-region is normally a disabled command. Attempting to use
this command asks for confirmation and gives you the option of enabling it;
if you enable the command, confirmation will no longer be required for
it. See Disabling.

14.6 View Mode

View mode is a minor mode that lets you scan a buffer by sequential
screenfuls. It provides commands for scrolling through the buffer
conveniently but not for changing it. Apart from the usual Emacs
cursor motion commands, you can type SPC to scroll forward one
windowful, S-SPC or DEL to scroll backward, and s to
start an incremental search.

Typing q (View-quit) disables View mode, and switches
back to the buffer and position before View mode was enabled. Typing
e (View-exit) disables View mode, keeping the current
buffer and position.

M-x view-buffer prompts for an existing Emacs buffer, switches
to it, and enables View mode. M-x view-file prompts for a file
and visits it with View mode enabled.

14.7 Follow Mode

Follow mode is a minor mode that makes two windows, both
showing the same buffer, scroll as a single tall “virtual window”.
To use Follow mode, go to a frame with just one window, split it into
two side-by-side windows using C-x 3, and then type M-x
follow-mode. From then on, you can edit the buffer in either of the
two windows, or scroll either one; the other window follows it.

In Follow mode, if you move point outside the portion visible in one
window and into the portion visible in the other window, that selects
the other window—again, treating the two as if they were parts of
one large window.

14.8 Text Faces

Emacs can display text in several different styles, called
faces. Each face can specify various face attributes,
such as the font, height, weight, slant, foreground and background
color, and underlining or overlining. Most major modes assign faces
to the text automatically, via Font Lock mode. See Font Lock, for
more information about how these faces are assigned.

To see what faces are currently defined, and what they look like,
type M-x list-faces-display. With a prefix argument, this
prompts for a regular expression, and displays only faces with names
matching that regular expression (see Regexps).

It’s possible for a given face to look different in different
frames. For instance, some text terminals do not support all face
attributes, particularly font, height, and width, and some support a
limited range of colors. In addition, most Emacs faces are defined so
that their attributes are different on light and dark frame
backgrounds, for reasons of legibility. By default, Emacs
automatically chooses which set of face attributes to display on each
frame, based on the frame’s current background color. However, you
can override this by giving the variable frame-background-mode
a non-nil value. A value of dark makes Emacs treat all
frames as if they have a dark background, whereas a value of
light makes it treat all frames as if they have a light
background.

You can customize a face to alter its attributes, and save those
customizations for future Emacs sessions. See Face Customization,
for details.

The default face is the default for displaying text, and all
of its attributes are specified. Its background color is also used as
the frame’s background color. See Colors.

Another special face is the cursor face. On graphical
displays, the background color of this face is used to draw the text
cursor. None of the other attributes of this face have any effect;
the foreground color for text under the cursor is taken from the
background color of the underlying text. On text terminals, the
appearance of the text cursor is determined by the terminal, not by
the cursor face.

You can also use X resources to specify attributes of any particular
face. See Resources.

Emacs can display variable-width fonts, but some Emacs commands,
particularly indentation commands, do not account for variable
character display widths. Therefore, we recommend not using
variable-width fonts for most faces, particularly those assigned by
Font Lock mode.

14.9 Colors for Faces

Faces can have various foreground and background colors. When you
specify a color for a face—for instance, when customizing the face
(see Face Customization)—you can use either a color name
or an RGB triplet.

A color name is a pre-defined name, such as ‘dark orange’ or
‘medium sea green’. To view a list of color names, type M-x
list-colors-display. To control the order in which colors are shown,
customize list-colors-sort. If you run this command on a
graphical display, it shows the full range of color names known to
Emacs (these are the standard X11 color names, defined in X’s
rgb.txt file). If you run the command on a text terminal, it
shows only a small subset of colors that can be safely displayed on
such terminals. However, Emacs understands X11 color names even on
text terminals; if a face is given a color specified by an X11 color
name, it is displayed using the closest-matching terminal color.

An RGB triplet is a string of the form ‘#RRGGBB’. Each of the
R, G, and B components is a hexadecimal number specifying the
component’s relative intensity, one to four digits long (usually two
digits are used). The components must have the same number of digits.
For hexadecimal values A to F, either upper or lower case are
acceptable.

The M-x list-colors-display command also shows the equivalent
RGB triplet for each named color. For instance, ‘medium sea
green’ is equivalent to ‘#3CB371’.

You can change the foreground and background colors of a face with
M-x set-face-foreground and M-x set-face-background.
These commands prompt in the minibuffer for a face name and a color,
with completion, and then set that face to use the specified color.
They affect the face colors on all frames, but their effects do not
persist for future Emacs sessions, unlike using the customization
buffer or X resources. You can also use frame parameters to set
foreground and background colors for a specific frame; See Frame Parameters.

14.10 Standard Faces

Here are the standard faces for specifying text appearance. You can
apply them to specific text when you want the effects they produce.

default

This face is used for ordinary text that doesn’t specify any face.
Its background color is used as the frame’s background color.

bold

This face uses a bold variant of the default font.

italic

This face uses an italic variant of the default font.

bold-italic

This face uses a bold italic variant of the default font.

underline

This face underlines text.

fixed-pitch

This face forces use of a fixed-width font. It’s reasonable to
customize this face to use a different fixed-width font, if you like,
but you should not make it a variable-width font.

variable-pitch

This face forces use of a variable-width font.

shadow

This face is used for making the text less noticeable than the surrounding
ordinary text. Usually this can be achieved by using shades of gray in
contrast with either black or white default foreground color.

Here’s an incomplete list of faces used to highlight parts of the
text temporarily for specific purposes. (Many other modes define
their own faces for this purpose.)

highlight

This face is used for text highlighting in various contexts, such as
when the mouse cursor is moved over a hyperlink.

The following faces control the appearance of parts of the Emacs
frame:

mode-line

This face is used for the mode line of the currently selected window,
and for menu bars when toolkit menus are not used. By default, it’s
drawn with shadows for a “raised” effect on graphical displays, and
drawn as the inverse of the default face on non-windowed terminals.

mode-line-inactive

Like mode-line, but used for mode lines of the windows other
than the selected one (if mode-line-in-non-selected-windows is
non-nil). This face inherits from mode-line, so changes
in that face affect mode lines in all windows.

mode-line-highlight

Like highlight, but used for mouse-sensitive portions of text
on mode lines. Such portions of text typically pop up tooltips
(see Tooltips) when the mouse pointer hovers above them.

mode-line-buffer-id

This face is used for buffer identification parts in the mode line.

header-line

Similar to mode-line for a window’s header line, which appears
at the top of a window just as the mode line appears at the bottom.
Most windows do not have a header line—only some special modes, such
Info mode, create one.

vertical-border

This face is used for the vertical divider between windows on text
terminals.

minibuffer-prompt

This face is used for the prompt strings displayed in the minibuffer.
By default, Emacs automatically adds this face to the value of
minibuffer-prompt-properties, which is a list of text
properties used to display the prompt text. (This variable takes
effect when you enter the minibuffer.)

fringe

The face for the fringes to the left and right of windows on graphic
displays. (The fringes are the narrow portions of the Emacs frame
between the text area and the window’s right and left borders.)
See Fringes.

cursor

The :background attribute of this face specifies the color of
the text cursor. See Cursor Display.

tooltip

This face is used for tooltip text. By default, if Emacs is built
with GTK support, tooltips are drawn via GTK and this face has no
effect. See Tooltips.

mouse

This face determines the color of the mouse pointer.

The following faces likewise control the appearance of parts of the
Emacs frame, but only on text terminals, or when Emacs is built on X
with no toolkit support. (For all other cases, the appearance of the
respective frame elements is determined by system-wide settings.)

scroll-bar

This face determines the visual appearance of the scroll bar.
See Scroll Bars.

14.11 Text Scale

To increase the height of the default face in the current buffer,
type C-x C-+ or C-x C-=. To decrease it, type C-x
C--. To restore the default (global) face height, type C-x
C-0. These keys are all bound to the same command,
text-scale-adjust, which looks at the last key typed to
determine which action to take.

The final key of these commands may be repeated without the leading
C-x. For instance, C-x C-= C-= C-= increases the face
height by three steps. Each step scales the text height by a factor
of 1.2; to change this factor, customize the variable
text-scale-mode-step. A numeric argument of 0
to the text-scale-adjust command restores the default height,
the same as typing C-x C-0.

The commands text-scale-increase and
text-scale-decrease increase or decrease the height of the
default face, just like C-x C-+ and C-x C-- respectively.
You may find it convenient to bind to these commands, rather than
text-scale-adjust.

The command text-scale-set scales the height of the default
face in the current buffer to an absolute level specified by its
prefix argument.

The above commands automatically enable the minor mode
text-scale-mode if the current font scaling is other than 1,
and disable it otherwise.

14.12 Font Lock mode

Font Lock mode is a minor mode, always local to a particular buffer,
which assigns faces to (or fontifies) the text in the buffer.
Each buffer’s major mode tells Font Lock mode which text to fontify;
for instance, programming language modes fontify syntactically
relevant constructs like comments, strings, and function names.

Font Lock mode is enabled by default. To toggle it in the current
buffer, type M-x font-lock-mode. A positive numeric argument
unconditionally enables Font Lock mode, and a negative or zero
argument disables it.

Type M-x global-font-lock-mode to toggle Font Lock mode in all
buffers. To impose this setting for future Emacs sessions, customize
the variable global-font-lock-mode (see Easy Customization), or add the following line to your init file:

(global-font-lock-mode 0)

If you have disabled Global Font Lock mode, you can still enable Font
Lock for specific major modes by adding the function
font-lock-mode to the mode hooks (see Hooks). For example,
to enable Font Lock mode for editing C files, you can do this:

(add-hook 'c-mode-hook 'font-lock-mode)

Font Lock mode uses several specifically named faces to do its job,
including font-lock-string-face, font-lock-comment-face,
and others. The easiest way to find them all is to use M-x
customize-group RET font-lock-faces RET. You can then
use that customization buffer to customize the appearance of these
faces. See Face Customization.

You can customize the variable font-lock-maximum-decoration
to alter the amount of fontification applied by Font Lock mode, for
major modes that support this feature. The value should be a number
(with 1 representing a minimal amount of fontification; some modes
support levels as high as 3); or t, meaning “as high as
possible” (the default). You can also specify different numbers for
particular major modes; for example, to use level 1 for C/C++ modes,
and the default level otherwise, use the value

'((c-mode . 1) (c++-mode . 1)))

Comment and string fontification (or “syntactic” fontification)
relies on analysis of the syntactic structure of the buffer text. For
the sake of speed, some modes, including Lisp mode, rely on a special
convention: an open-parenthesis or open-brace in the leftmost column
always defines the beginning of a defun, and is thus always outside
any string or comment. Therefore, you should avoid placing an
open-parenthesis or open-brace in the leftmost column, if it is inside
a string or comment. See Left Margin Paren, for details.

The variable font-lock-beginning-of-syntax-function, which is
always buffer-local, specifies how Font Lock mode can find a position
guaranteed to be outside any comment or string. In modes which use
the leftmost column parenthesis convention, the default value of the
variable is beginning-of-defun—that tells Font Lock mode to
use the convention. If you set this variable to nil, Font Lock
no longer relies on the convention. This avoids incorrect results,
but the price is that, in some cases, fontification for a changed text
must rescan buffer text from the beginning of the buffer. This can
considerably slow down redisplay while scrolling, particularly if you
are close to the end of a large buffer.

Font Lock highlighting patterns already exist for most modes, but
you may want to fontify additional patterns. You can use the function
font-lock-add-keywords, to add your own highlighting patterns
for a particular mode. For example, to highlight ‘FIXME:’ words
in C comments, use this:

To remove keywords from the font-lock highlighting patterns, use the
function font-lock-remove-keywords. See Search-based
Fontification in The Emacs Lisp Reference Manual.

Fontifying large buffers can take a long time. To avoid large
delays when a file is visited, Emacs initially fontifies only the
visible portion of a buffer. As you scroll through the buffer, each
portion that becomes visible is fontified as soon as it is displayed;
this type of Font Lock is called Just-In-Time (or JIT)
Lock. You can control how JIT Lock behaves, including telling it to
perform fontification while idle, by customizing variables in the
customization group ‘jit-lock’. See Specific Customization.

14.13 Interactive Highlighting

Highlight Changes mode is a minor mode that highlights the parts
of the buffer that were changed most recently, by giving that text a
different face. To enable or disable Highlight Changes mode, use
M-x highlight-changes-mode.

Hi Lock mode is a minor mode that highlights text that matches
regular expressions you specify. For example, you can use it to
highlight all the references to a certain variable in a program source
file, highlight certain parts in a voluminous output of some program,
or highlight certain names in an article. To enable or disable Hi
Lock mode, use the command M-x hi-lock-mode. To enable Hi Lock
mode for all buffers, use M-x global-hi-lock-mode or place
(global-hi-lock-mode 1) in your .emacs file.

Hi Lock mode works like Font Lock mode (see Font Lock), except
that you specify explicitly the regular expressions to highlight. You
control them with these commands:

M-s h r regexpRETfaceRET

C-x w h regexpRETfaceRET

Highlight text that matches regexp using face face
(highlight-regexp). The highlighting will remain as long as
the buffer is loaded. For example, to highlight all occurrences of
the word “whim” using the default face (a yellow background)
M-s h r whim RETRET. Any face can be used for
highlighting, Hi Lock provides several of its own and these are
pre-loaded into a list of default values. While being prompted
for a face use M-n and M-p to cycle through them.

Setting the option hi-lock-auto-select-face to a non-nil
value causes this command (and other Hi Lock commands that read faces)
to automatically choose the next face from the default list without
prompting.

You can use this command multiple times, specifying various regular
expressions to highlight in different ways.

M-s h u regexpRET

C-x w r regexpRET

Unhighlight regexp (unhighlight-regexp).

If you invoke this from the menu, you select the expression to
unhighlight from a list. If you invoke this from the keyboard, you
use the minibuffer. It will show the most recently added regular
expression; use M-n to show the next older expression and
M-p to select the next newer expression. (You can also type the
expression by hand, with completion.) When the expression you want to
unhighlight appears in the minibuffer, press RET to exit
the minibuffer and unhighlight it.

Highlight matches of phrase, using face face
(highlight-phrase). phrase can be any regexp,
but spaces will be replaced by matches to whitespace and
initial lower-case letters will become case insensitive.

M-s h .

C-x w .

Highlight the symbol found near point, using the next available face
(highlight-symbol-at-point).

M-s h w

C-x w b

Insert all the current highlighting regexp/face pairs into the buffer
at point, with comment delimiters to prevent them from changing your
program. (This key binding runs the
hi-lock-write-interactive-patterns command.)

These patterns are extracted from the comments, if appropriate, if you
invoke M-x hi-lock-find-patterns, or if you visit the file while
Hi Lock mode is enabled (since that runs hi-lock-find-patterns).

M-s h f

C-x w i

Extract regexp/face pairs from comments in the current buffer
(hi-lock-find-patterns). Thus, you can enter patterns
interactively with highlight-regexp, store them into the file
with hi-lock-write-interactive-patterns, edit them (perhaps
including different faces for different parenthesized parts of the
match), and finally use this command (hi-lock-find-patterns) to
have Hi Lock highlight the edited patterns.

The variable hi-lock-file-patterns-policy controls whether Hi
Lock mode should automatically extract and highlight patterns found in a
file when it is visited. Its value can be nil (never highlight),
ask (query the user), or a function. If it is a function,
hi-lock-find-patterns calls it with the patterns as argument; if
the function returns non-nil, the patterns are used. The default
is ask. Note that patterns are always highlighted if you call
hi-lock-find-patterns directly, regardless of the value of this
variable.

Also, hi-lock-find-patterns does nothing if the current major
mode’s symbol is a member of the list hi-lock-exclude-modes.

14.14 Window Fringes

On graphical displays, each Emacs window normally has narrow
fringes on the left and right edges. The fringes are used to
display symbols that provide information about the text in the window.
You can type M-x fringe-mode to disable the fringes, or modify
their width. This command affects fringes in all frames; to modify
fringes on the selected frame only, use M-x set-fringe-style.
You can make your changes to the fringes permanent by customizing the
variable fringe-mode.

The most common use of the fringes is to indicate a continuation
line (see Continuation Lines). When one line of text is split
into multiple screen lines, the left fringe shows a curving arrow for
each screen line except the first, indicating that “this is not the
real beginning”. The right fringe shows a curving arrow for each
screen line except the last, indicating that “this is not the real
end”. If the line’s direction is right-to-left (see Bidirectional Editing), the meanings of the curving arrows in the fringes are
swapped.

The fringes indicate line truncation with short horizontal arrows
meaning “there’s more text on this line which is scrolled
horizontally out of view”. Clicking the mouse on one of the arrows
scrolls the display horizontally in the direction of the arrow.

The fringes can also indicate other things, such as buffer
boundaries (see Displaying Boundaries), and where a program you
are debugging is executing (see Debuggers).

The fringe is also used for drawing the cursor, if the current line
is exactly as wide as the window and point is at the end of the line.
To disable this, change the variable
overflow-newline-into-fringe to nil; this causes Emacs
to continue or truncate lines that are exactly as wide as the window.

14.15 Displaying Boundaries

On graphical displays, Emacs can indicate the buffer boundaries in
the fringes. If you enable this feature, the first line and the last
line are marked with angle images in the fringes. This can be
combined with up and down arrow images which say whether it is
possible to scroll the window.

The buffer-local variable indicate-buffer-boundaries controls
how the buffer boundaries and window scrolling is indicated in the
fringes. If the value is left or right, both angle and
arrow bitmaps are displayed in the left or right fringe, respectively.

If value is an alist, each element (indicator .
position) specifies the position of one of the indicators.
The indicator must be one of top, bottom,
up, down, or t which specifies the default
position for the indicators not present in the alist.
The position is one of left, right, or nil
which specifies not to show this indicator.

For example, ((top . left) (t . right)) places the top angle
bitmap in left fringe, the bottom angle bitmap in right fringe, and
both arrow bitmaps in right fringe. To show just the angle bitmaps in
the left fringe, but no arrow bitmaps, use ((top . left)
(bottom . left)).

14.16 Useless Whitespace

It is easy to leave unnecessary spaces at the end of a line, or
empty lines at the end of a buffer, without realizing it. In most
cases, this trailing whitespace has no effect, but sometimes it
can be a nuisance.

You can make trailing whitespace at the end of a line visible by
setting the buffer-local variable show-trailing-whitespace to
t. Then Emacs displays trailing whitespace, using the face
trailing-whitespace.

This feature does not apply when point is at the end of the line
containing the whitespace. Strictly speaking, that is “trailing
whitespace” nonetheless, but displaying it specially in that case
looks ugly while you are typing in new text. In this special case,
the location of point is enough to show you that the spaces are
present.

Type M-x delete-trailing-whitespace to delete all trailing
whitespace. This command deletes all extra spaces at the end of each
line in the buffer, and all empty lines at the end of the buffer; to
ignore the latter, change the variable delete-trailing-lines to
nil. If the region is active, the command instead deletes
extra spaces at the end of each line in the region.

On graphical displays, Emacs can indicate unused lines at the end of
the window with a small image in the left fringe (see Fringes).
The image appears for screen lines that do not correspond to any
buffer text, so blank lines at the end of the buffer stand out because
they lack this image. To enable this feature, set the buffer-local
variable indicate-empty-lines to a non-nil value. You
can enable or disable this feature for all new buffers by setting the
default value of this variable, e.g., (setq-default
indicate-empty-lines t).

Whitespace mode is a buffer-local minor mode that lets you
“visualize” many kinds of whitespace in the buffer, by either
drawing the whitespace characters with a special face or displaying
them as special glyphs. To toggle this mode, type M-x
whitespace-mode. The kinds of whitespace visualized are determined
by the list variable whitespace-style. Here is a partial list
of possible elements (see the variable’s documentation for the full
list):

face

Enable all visualizations which use special faces. This element has a
special meaning: if it is absent from the list, none of the other
visualizations take effect except space-mark, tab-mark,
and newline-mark.

14.17 Selective Display

Emacs has the ability to hide lines indented more than a given
number of columns. You can use this to get an overview of a part of a
program.

To hide lines in the current buffer, type C-x $
(set-selective-display) with a numeric argument n. Then
lines with at least n columns of indentation disappear from the
screen. The only indication of their presence is that three dots
(‘…’) appear at the end of each visible line that is
followed by one or more hidden ones.

The commands C-n and C-p move across the hidden lines as
if they were not there.

The hidden lines are still present in the buffer, and most editing
commands see them as usual, so you may find point in the middle of the
hidden text. When this happens, the cursor appears at the end of the
previous line, after the three dots. If point is at the end of the
visible line, before the newline that ends it, the cursor appears before
the three dots.

To make all lines visible again, type C-x $ with no argument.

If you set the variable selective-display-ellipses to
nil, the three dots do not appear at the end of a line that
precedes hidden lines. Then there is no visible indication of the
hidden lines. This variable becomes local automatically when set.

See also Outline Mode for another way to hide part of
the text in a buffer.

14.18 Optional Mode Line Features

The buffer percentage pos indicates the percentage of the
buffer above the top of the window. You can additionally display the
size of the buffer by typing M-x size-indication-mode to turn on
Size Indication mode. The size will be displayed immediately
following the buffer percentage like this:

pos of size

Here size is the human readable representation of the number of
characters in the buffer, which means that ‘k’ for 10^3, ‘M’
for 10^6, ‘G’ for 10^9, etc., are used to abbreviate.

The current line number of point appears in the mode line when Line
Number mode is enabled. Use the command M-x line-number-mode to
turn this mode on and off; normally it is on. The line number appears
after the buffer percentage pos, with the letter ‘L’ to
indicate what it is.

Similarly, you can display the current column number by turning on
Column number mode with M-x column-number-mode. The column
number is indicated by the letter ‘C’. However, when both of
these modes are enabled, the line and column numbers are displayed in
parentheses, the line number first, rather than with ‘L’ and
‘C’. For example: ‘(561,2)’. See Minor Modes, for more
information about minor modes and about how to use these commands.

If you have narrowed the buffer (see Narrowing), the displayed
line number is relative to the accessible portion of the buffer.
Thus, it isn’t suitable as an argument to goto-line. (Use
what-line command to see the line number relative to the whole
file.)

If the buffer is very large (larger than the value of
line-number-display-limit), Emacs won’t compute the line
number, because that would be too slow; therefore, the line number
won’t appear on the mode-line. To remove this limit, set
line-number-display-limit to nil.

Line-number computation can also be slow if the lines in the buffer
are too long. For this reason, Emacs doesn’t display line numbers if
the average width, in characters, of lines near point is larger than
the value of line-number-display-limit-width. The default
value is 200 characters.

Emacs can optionally display the time and system load in all mode
lines. To enable this feature, type M-x display-time or customize
the option display-time-mode. The information added to the mode
line looks like this:

hh:mmpm l.ll

Here hh and mm are the hour and minute, followed always by
‘am’ or ‘pm’. l.ll is the average number, collected
for the last few minutes, of processes in the whole system that were
either running or ready to run (i.e., were waiting for an available
processor). (Some fields may be missing if your operating system
cannot support them.) If you prefer time display in 24-hour format,
set the variable display-time-24hr-format to t.

The word ‘Mail’ appears after the load level if there is mail
for you that you have not read yet. On graphical displays, you can
use an icon instead of ‘Mail’ by customizing
display-time-use-mail-icon; this may save some space on the
mode line. You can customize display-time-mail-face to make
the mail indicator prominent. Use display-time-mail-file to
specify the mail file to check, or set
display-time-mail-directory to specify the directory to check
for incoming mail (any nonempty regular file in the directory is
considered as “newly arrived mail”).

When running Emacs on a laptop computer, you can display the battery
charge on the mode-line, by using the command
display-battery-mode or customizing the variable
display-battery-mode. The variable
battery-mode-line-format determines the way the battery charge
is displayed; the exact mode-line message depends on the operating
system, and it usually shows the current battery charge as a
percentage of the total charge.

On graphical displays, the mode line is drawn as a 3D box. If you
don’t like this effect, you can disable it by customizing the
mode-line face and setting its box attribute to
nil. See Face Customization.

By default, the mode line of nonselected windows is displayed in a
different face, called mode-line-inactive. Only the selected
window is displayed in the mode-line face. This helps show
which window is selected. When the minibuffer is selected, since
it has no mode line, the window from which you activated the minibuffer
has its mode line displayed using mode-line; as a result,
ordinary entry to the minibuffer does not change any mode lines.

You can disable use of mode-line-inactive by setting variable
mode-line-in-non-selected-windows to nil; then all mode
lines are displayed in the mode-line face.

You can customize the mode line display for each of the end-of-line
formats by setting each of the variables eol-mnemonic-unix,
eol-mnemonic-dos, eol-mnemonic-mac, and
eol-mnemonic-undecided to the strings you prefer.

14.19 How Text Is Displayed

Most characters are printing characters: when they appear in a
buffer, they are displayed literally on the screen. Printing
characters include ASCII numbers, letters, and punctuation
characters, as well as many non-ASCII characters.

The ASCII character set contains non-printing control
characters. Two of these are displayed specially: the newline
character (Unicode code point U+000A) is displayed by starting
a new line, while the tab character (U+0009) is displayed as a
space that extends to the next tab stop column (normally every 8
columns). The number of spaces per tab is controlled by the
buffer-local variable tab-width, which must have an integer
value between 1 and 1000, inclusive. Note that how the tab character
in the buffer is displayed has nothing to do with the definition of
TAB as a command.

Other ASCII control characters, whose codes are below
U+0020 (octal 40, decimal 32), are displayed as a caret
(‘^’) followed by the non-control version of the character, with
the escape-glyph face. For instance, the ‘control-A’
character, U+0001, is displayed as ‘^A’.

The raw bytes with codes U+0080 (octal 200) through
U+009F (octal 237) are displayed as octal escape
sequences, with the escape-glyph face. For instance,
character code U+0098 (octal 230) is displayed as ‘\230’.
If you change the buffer-local variable ctl-arrow to
nil, the ASCII control characters are also displayed
as octal escape sequences instead of caret escape sequences.

Some non-ASCII characters have the same appearance as an
ASCII space or hyphen (minus) character. Such characters
can cause problems if they are entered into a buffer without your
realization, e.g., by yanking; for instance, source code compilers
typically do not treat non-ASCII spaces as whitespace
characters. To deal with this problem, Emacs displays such characters
specially: it displays U+00A0 (no-break space) with the
nobreak-space face, and it displays U+00AD (soft
hyphen), U+2010 (hyphen), and U+2011 (non-breaking
hyphen) with the escape-glyph face. To disable this, change
the variable nobreak-char-display to nil. If you give
this variable a non-nil and non-t value, Emacs instead
displays such characters as a highlighted backslash followed by a
space or hyphen.

You can customize the way any particular character code is displayed
by means of a display table. See Display Tables in The Emacs Lisp Reference Manual.

On graphical displays, some characters may have no glyphs in any of
the fonts available to Emacs. These glyphless characters are
normally displayed as boxes containing the hexadecimal character code.
Similarly, on text terminals, characters that cannot be displayed
using the terminal encoding (see Terminal Coding) are normally
displayed as question signs. You can control the display method by
customizing the variable glyphless-char-display-control.
See Glyphless Character Display in The Emacs
Lisp Reference Manual, for details.

14.20 Displaying the Cursor

On a text terminal, the cursor’s appearance is controlled by the
terminal, largely out of the control of Emacs. Some terminals offer
two different cursors: a “visible” static cursor, and a “very
visible” blinking cursor. By default, Emacs uses the very visible
cursor, and switches to it when you start or resume Emacs. If the
variable visible-cursor is nil when Emacs starts or
resumes, it uses the normal cursor.

On a graphical display, many more properties of the text cursor can
be altered. To customize its color, change the :background
attribute of the face named cursor (see Face Customization). (The other attributes of this face have no effect;
the text shown under the cursor is drawn using the frame’s background
color.) To change its shape, customize the buffer-local variable
cursor-type; possible values are box (the default),
hollow (a hollow box), bar (a vertical bar), (bar
. n) (a vertical bar n pixels wide), hbar (a
horizontal bar), (hbar . n) (a horizontal bar n
pixels tall), or nil (no cursor at all).

By default, the cursor stops blinking after 10 blinks, if Emacs does
not get any input during that time; any input event restarts the
count. You can customize the variable blink-cursor-blinks to
control that: its value says how many times to blink without input
before stopping. Setting that variable to a zero or negative value
will make the cursor blink forever. To disable cursor blinking
altogether, change the variable blink-cursor-mode to nil
(see Easy Customization), or add the line

(blink-cursor-mode 0)

to your init file. Alternatively, you can change how the cursor
looks when it “blinks off” by customizing the list variable
blink-cursor-alist. Each element in the list should have the
form (on-type . off-type); this means that if the
cursor is displayed as on-type when it blinks on (where
on-type is one of the cursor types described above), then it is
displayed as off-type when it blinks off.

Some characters, such as tab characters, are “extra wide”. When
the cursor is positioned over such a character, it is normally drawn
with the default character width. You can make the cursor stretch to
cover wide characters, by changing the variable
x-stretch-cursor to a non-nil value.

The cursor normally appears in non-selected windows as a
non-blinking hollow box. (For a bar cursor, it instead appears as a
thinner bar.) To turn off cursors in non-selected windows, change the
variable cursor-in-non-selected-windows to nil.

To make the cursor even more visible, you can use HL Line mode, a
minor mode that highlights the line containing point. Use M-x
hl-line-mode to enable or disable it in the current buffer. M-x
global-hl-line-mode enables or disables the same mode globally.

14.21 Line Truncation

As an alternative to continuation (see Continuation Lines),
Emacs can display long lines by truncation. This means that all
the characters that do not fit in the width of the screen or window do
not appear at all. On graphical displays, a small straight arrow in
the fringe indicates truncation at either end of the line. On text
terminals, this is indicated with ‘$’ signs in the leftmost
and/or rightmost columns.

Horizontal scrolling automatically causes line truncation
(see Horizontal Scrolling). You can explicitly enable line
truncation for a particular buffer with the command M-x
toggle-truncate-lines. This works by locally changing the variable
truncate-lines. If that variable is non-nil, long lines
are truncated; if it is nil, they are continued onto multiple
screen lines. Setting the variable truncate-lines in any way
makes it local to the current buffer; until that time, the default
value, which is normally nil, is in effect.

If a split window becomes too narrow, Emacs may automatically enable
line truncation. See Split Window, for the variable
truncate-partial-width-windows which controls this.

14.22 Visual Line Mode

Another alternative to ordinary line continuation is to use
word wrap. Here, each long logical line is divided into two or
more screen lines, like in ordinary line continuation. However, Emacs
attempts to wrap the line at word boundaries near the right window
edge. This makes the text easier to read, as wrapping does not occur
in the middle of words.

Word wrap is enabled by Visual Line mode, an optional minor mode.
To turn on Visual Line mode in the current buffer, type M-x
visual-line-mode; repeating this command turns it off. You can also
turn on Visual Line mode using the menu bar: in the Options menu,
select the ‘Line Wrapping in this Buffer’ submenu, followed by
the ‘Word Wrap (Visual Line Mode)’ menu item. While Visual Line
mode is enabled, the mode-line shows the string ‘wrap’ in the
mode display. The command M-x global-visual-line-mode toggles
Visual Line mode in all buffers.

In Visual Line mode, some editing commands work on screen lines
instead of logical lines: C-a (beginning-of-visual-line)
moves to the beginning of the screen line, C-e
(end-of-visual-line) moves to the end of the screen line, and
C-k (kill-visual-line) kills text to the end of the
screen line.

To move by logical lines, use the commands M-x
next-logical-line and M-x previous-logical-line. These move
point to the next logical line and the previous logical line
respectively, regardless of whether Visual Line mode is enabled. If
you use these commands frequently, it may be convenient to assign key
bindings to them. See Init Rebinding.

By default, word-wrapped lines do not display fringe indicators.
Visual Line mode is often used to edit files that contain many long
logical lines, so having a fringe indicator for each wrapped line
would be visually distracting. You can change this by customizing the
variable visual-line-fringe-indicators.

14.23 Customization of Display

This section describes variables that control miscellaneous aspects
of the appearance of the Emacs screen. Beginning users can skip it.

If the variable visible-bell is non-nil, Emacs attempts
to make the whole screen blink when it would normally make an audible bell
sound. This variable has no effect if your terminal does not have a way
to make the screen blink.

The variable echo-keystrokes controls the echoing of multi-character
keys; its value is the number of seconds of pause required to cause echoing
to start, or zero, meaning don’t echo at all. The value takes effect when
there is something to echo. See Echo Area.

On graphical displays, Emacs displays the mouse pointer as an
hourglass if Emacs is busy. To disable this feature, set the variable
display-hourglass to nil. The variable
hourglass-delay determines the number of seconds of “busy
time” before the hourglass is shown; the default is 1.

If the mouse pointer lies inside an Emacs frame, Emacs makes it
invisible each time you type a character to insert text, to prevent it
from obscuring the text. (To be precise, the hiding occurs when you
type a “self-inserting” character. See Inserting Text.) Moving
the mouse pointer makes it visible again. To disable this feature,
set the variable make-pointer-invisible to nil.

On graphical displays, the variable underline-minimum-offset
determines the minimum distance between the baseline and underline, in
pixels, for underlined text. By default, the value is 1; increasing
it may improve the legibility of underlined text for certain fonts.
(However, Emacs will never draw the underline below the current line
area.) The variable x-underline-at-descent-line determines how
to draw underlined text. The default is nil, which means to
draw it at the baseline level of the font; if you change it to
nil, Emacs draws the underline at the same height as the font’s
descent line.

The variable overline-margin specifies the vertical position
of an overline above the text, including the height of the overline
itself, in pixels; the default is 2.

On some text terminals, bold face and inverse video together result
in text that is hard to read. Call the function
tty-suppress-bold-inverse-default-colors with a non-nil
argument to suppress the effect of bold-face in this case.

15 Searching and Replacement

Like other editors, Emacs has commands to search for occurrences of
a string. Emacs also has commands to replace occurrences of a string
with a different string. There are also commands that do the same
thing, but search for patterns instead of fixed strings.

15.1 Incremental Search

The principal search command in Emacs is incremental: it
begins searching as soon as you type the first character of the search
string. As you type in the search string, Emacs shows you where the
string (as you have typed it so far) would be found. When you have
typed enough characters to identify the place you want, you can stop.
Depending on what you plan to do next, you may or may not need to
terminate the search explicitly with RET.

15.1.1 Basics of Incremental Search

C-s (isearch-forward) starts a forward incremental
search. It reads characters from the keyboard, and moves point just
past the end of the next occurrence of those characters in the buffer.

For instance, if you type C-s and then F, that puts the
cursor after the first ‘F’ that occurs in the buffer after the
starting point. Then if you then type O, the cursor moves to
just after the first ‘FO’; the ‘F’ in that ‘FO’ might
not be the first ‘F’ previously found. After another O,
the cursor moves to just after the first ‘FOO’.

At each step, Emacs highlights the current match—the buffer
text that matches the search string—using the isearch face
(see Faces). The current search string is also displayed in the
echo area.

If you make a mistake typing the search string, type DEL.
Each DEL cancels the last character of the search string.

When you are satisfied with the place you have reached, type
RET. This stops searching, leaving the cursor where the search
brought it. Also, any command not specially meaningful in searches
stops the searching and is then executed. Thus, typing C-a
exits the search and then moves to the beginning of the line.
RET is necessary only if the next command you want to type is a
printing character, DEL, RET, or another character that is
special within searches (C-q, C-w, C-r, C-s,
C-y, M-y, M-r, M-c, M-e, and some others
described below).

As a special exception, entering RET when the search string is
empty launches nonincremental search (see Nonincremental Search).

When you exit the incremental search, it adds the original value of
point to the mark ring, without activating the mark; you can thus use
C-u C-SPC to return to where you were before beginning the
search. See Mark Ring. It only does this if the mark was not
already active.

To search backwards, use C-r (isearch-backward) instead
of C-s to start the search. A backward search finds matches
that end before the starting point, just as a forward search finds
matches that begin after it.

15.1.2 Repeating Incremental Search

Suppose you search forward for ‘FOO’ and find a match, but not
the one you expected to find: the ‘FOO’ you were aiming for
occurs later in the buffer. In this event, type another C-s to
move to the next occurrence of the search string. You can repeat this
any number of times. If you overshoot, you can cancel some C-s
characters with DEL. Similarly, each C-r in a backward
incremental search repeats the backward search.

If you pause for a little while during incremental search, Emacs
highlights all the other possible matches for the search string that
are present on the screen. This helps you anticipate where you can
get to by typing C-s or C-r to repeat the search. The
other matches are highlighted differently from the current match,
using the customizable face lazy-highlight (see Faces). If
you don’t like this feature, you can disable it by setting
isearch-lazy-highlight to nil.

After exiting a search, you can search for the same string again by
typing just C-s C-s. The first C-s is the key that
invokes incremental search, and the second C-s means “search
again”. Similarly, C-r C-r searches backward for the last
search string. In determining the last search string, it doesn’t
matter whether the string was searched for with C-s or
C-r.

If you are searching forward but you realize you were looking for
something before the starting point, type C-r to switch to a
backward search, leaving the search string unchanged. Similarly,
C-s in a backward search switches to a forward search.

If a search is failing and you ask to repeat it by typing another
C-s, it starts again from the beginning of the buffer.
Repeating a failing reverse search with C-r starts again from
the end. This is called wrapping around, and ‘Wrapped’
appears in the search prompt once this has happened. If you keep on
going past the original starting point of the search, it changes to
‘Overwrapped’, which means that you are revisiting matches that
you have already seen.

To reuse earlier search strings, use the search ring. The
commands M-p and M-n move through the ring to pick a
search string to reuse. These commands leave the selected search ring
element in the minibuffer, where you can edit it.

To edit the current search string in the minibuffer without
replacing it with items from the search ring, type M-e. Type RET,
C-s or C-r to finish editing the string and search for it.

15.1.3 Errors in Incremental Search

If your string is not found at all, the echo area says ‘Failing
I-Search’, and the cursor moves past the place where Emacs found as
much of your string as it could. Thus, if you search for ‘FOOT’,
and there is no ‘FOOT’, you might see the cursor after the
‘FOO’ in ‘FOOL’. In the echo area, the part of the search
string that failed to match is highlighted using the face
isearch-fail.

At this point, there are several things you can do. If your string
was mistyped, you can use DEL to erase some of it and correct
it. If you like the place you have found, you can type RET to
remain there. Or you can type C-g, which removes from the
search string the characters that could not be found (the ‘T’ in
‘FOOT’), leaving those that were found (the ‘FOO’ in
‘FOOT’). A second C-g at that point cancels the search
entirely, returning point to where it was when the search started.

The quit command, C-g, does special things during searches;
just what it does depends on the status of the search. If the search
has found what you specified and is waiting for input, C-g
cancels the entire search, moving the cursor back to where you started
the search. If C-g is typed when there are characters in the
search string that have not been found—because Emacs is still
searching for them, or because it has failed to find them—then the
search string characters which have not been found are discarded from
the search string. With them gone, the search is now successful and
waiting for more input, so a second C-g will cancel the entire
search.

15.1.4 Special Input for Incremental Search

Some of the characters you type during incremental search have
special effects.

By default, incremental search performs lax space matching:
each space, or sequence of spaces, matches any sequence of one or more
spaces in the text. Hence, ‘foo bar’ matches ‘foo bar’,
‘foo bar’, ‘foo bar’, and so on (but not ‘foobar’).
More precisely, Emacs matches each sequence of space characters in the
search string to a regular expression specified by the variable
search-whitespace-regexp. For example, to make spaces match
sequences of newlines as well as spaces, set it to
‘"[[:space:]\n]+"’.

To toggle lax space matching, type M-s SPC
(isearch-toggle-lax-whitespace). To disable this feature
entirely, change search-whitespace-regexp to nil; then
each space in the search string matches exactly one space.

If the search string you entered contains only lower-case letters,
the search is case-insensitive; as long as an upper-case letter exists
in the search string, the search becomes case-sensitive. If you
delete the upper-case character from the search string, it ceases to
have this effect. See Search Case.

To toggle whether or not invisible text is searched, type
M-s i (isearch-toggle-invisible). See Outline Search.

To search for a newline character, type C-j.

To search for non-ASCII characters, use one of the
following methods:

Type C-q, followed by a non-graphic character or a sequence of
octal digits. This adds a character to the search string, similar to
inserting into a buffer using C-q (see Inserting Text). For
example, C-q C-s during incremental search adds the
‘control-S’ character to the search string.

Type C-x 8 RET, followed by a Unicode name or code-point.
This adds the specified character into the search string, similar to
the usual insert-char command (see Inserting Text).

Use an input method (see Input Methods). If an input method is
enabled in the current buffer when you start the search, you can use
it in the search string also. While typing the search string, you can
toggle the input method with C-\
(isearch-toggle-input-method). You can also turn on a
non-default input method with C-^
(isearch-toggle-specified-input-method), which prompts for the
name of the input method. When an input method is active during
incremental search, the search prompt includes the input method
mnemonic, like this:

I-search [im]:

where im is the mnemonic of the active input method. Any input
method you enable during incremental search remains enabled in the
current buffer afterwards.

Typing M-% in incremental search invokes query-replace
or query-replace-regexp (depending on search mode) with the
current search string used as the string to replace. A negative
prefix argument means to replace backward. See Query Replace.

Typing M-TAB in incremental search invokes
isearch-complete, which attempts to complete the search string
using the search ring as a list of completion alternatives.
See Completion. In many operating systems, the M-TAB
key sequence is captured by the window manager; you then need to
rebind isearch-complete to another key sequence if you want to
use it (see Rebinding).

When incremental search is active, you can type C-h C-h to
access interactive help options, including a list of special key
bindings. These key bindings are part of the keymap
isearch-mode-map (see Keymaps).

15.1.5 Isearch Yanking

Within incremental search, C-y (isearch-yank-kill)
appends the current kill to the search string. M-y
(isearch-yank-pop), if called after C-y, replaces that
appended text with an earlier kill, similar to the usual M-y
(yank-pop) command (see Yanking). Mouse-2 appends
the current X selection (see Primary Selection).

C-w (isearch-yank-word-or-char) appends the next
character or word at point to the search string. This is an easy way
to search for another occurrence of the text at point. (The decision
of whether to copy a character or a word is heuristic.)

Similarly, M-s C-e (isearch-yank-line) appends the rest
of the current line to the search string. If point is already at the
end of a line, it appends the next line. With a prefix argument
n, it appends the next n lines.

If the search is currently case-insensitive, both C-w and
M-s C-e convert the text they copy to lower case, so that the
search remains case-insensitive.

C-M-w (isearch-del-char) deletes the last character
from the search string, and C-M-y (isearch-yank-char)
appends the character after point to the search string. An
alternative method to add the character after point is to enter the
minibuffer with M-e (see Repeat Isearch) and type C-f
at the end of the search string in the minibuffer.

15.1.6 Not Exiting Incremental Search

This subsection describes two categories of commands which you can
type without exiting the current incremental search, even though they
are not themselves part of incremental search.

Prefix Arguments

In incremental search, when you enter a prefix argument
(see Arguments), by default it will apply either to the next
action in the search or to the command that exits the search.

In previous versions of Emacs, entering a prefix argument always
terminated the search. You can revert to this behavior by setting the
variable isearch-allow-prefix to nil.

When isearch-allow-scroll is non-nil (see below),
prefix arguments always have the default behavior described above.

Scrolling Commands

Normally, scrolling commands exit incremental search. If you change
the variable isearch-allow-scroll to a non-nil value,
that enables the use of the scroll-bar, as well as keyboard scrolling
commands like C-v, M-v, and C-l (see Scrolling).
This applies only to calling these commands via their bound key
sequences—typing M-x will still exit the search. You can give
prefix arguments to these commands in the usual way. This feature
won’t let you scroll the current match out of visibility, however.

The isearch-allow-scroll feature also affects some other
commands, such as C-x 2 (split-window-below) and C-x
^ (enlarge-window), which don’t exactly scroll but do affect
where the text appears on the screen. It applies to any command whose
name has a non-nilisearch-scroll property. So you can
control which commands are affected by changing these properties.

For example, to make C-h l usable within an incremental search
in all future Emacs sessions, use C-h c to find what command it
runs (see Key Help), which is view-lossage. Then you can
put the following line in your init file (see Init File):

(put 'view-lossage 'isearch-scroll t)

This feature can be applied to any command that doesn’t permanently
change point, the buffer contents, the match data, the current buffer,
or the selected window and frame. The command must not itself attempt
an incremental search.

15.1.7 Searching the Minibuffer

If you start an incremental search while the minibuffer is active,
Emacs searches the contents of the minibuffer. Unlike searching an
ordinary buffer, the search string is not shown in the echo area,
because that is used to display the minibuffer.

If an incremental search fails in the minibuffer, it tries searching
the minibuffer history. See Minibuffer History. You can visualize
the minibuffer and its history as a series of “pages”, with the
earliest history element on the first page and the current minibuffer
on the last page. A forward search, C-s, searches forward to
later pages; a reverse search, C-r, searches backwards to
earlier pages. Like in ordinary buffer search, a failing search can
wrap around, going from the last page to the first page or vice versa.

When the current match is on a history element, that history element
is pulled into the minibuffer. If you exit the incremental search
normally (e.g., by typing RET), it remains in the minibuffer
afterwards. Canceling the search, with C-g, restores the
contents of the minibuffer when you began the search.

15.2 Nonincremental Search

Emacs also has conventional nonincremental search commands, which require
you to type the entire search string before searching begins.

C-s RETstringRET

Search for string.

C-r RETstringRET

Search backward for string.

To start a nonincremental search, first type C-s RET.
This enters the minibuffer to read the search string; terminate the
string with RET, and then the search takes place. If the string
is not found, the search command signals an error.

When you type C-s RET, the C-s invokes incremental
search as usual. That command is specially programmed to invoke the
command for nonincremental search, search-forward, if the
string you specify is empty. (Such an empty argument would otherwise
be useless.) C-r RET does likewise, invoking the command
search-backward.

15.3 Word Search

A word search finds a sequence of words without regard to the
type of punctuation between them. For instance, if you enter a search
string that consists of two words separated by a single space, the
search matches any sequence of those two words separated by one or
more spaces, newlines, or other punctuation characters. This is
particularly useful for searching text documents, because you don’t
have to worry whether the words you are looking for are separated by
newlines or spaces.

To begin a forward incremental word search, type M-s w. If
incremental search is not already active, this runs the command
isearch-forward-word. If incremental search is already active
(whether a forward or backward search), M-s w switches to a word
search while keeping the direction of the search and the current
search string unchanged. You can toggle word search back off by
typing M-s w again.

To begin a nonincremental word search, type M-s w RET
for a forward search, or M-s w C-r RET for a backward search.
These run the commands word-search-forward and
word-search-backward respectively.

Incremental and nonincremental word searches differ slightly in the
way they find a match. In a nonincremental word search, each word in
the search string must exactly match a whole word. In an incremental
word search, the matching is more lax: while you are typing the search
string, its first and last words need not match whole words. This is
so that the matching can proceed incrementally as you type. This
additional laxity does not apply to the lazy highlight, which always
matches whole words.

15.4 Symbol Search

A symbol search is much like an ordinary search, except that
the boundaries of the search must match the boundaries of a symbol.
The meaning of symbol in this context depends on the major mode,
and usually refers to a source code token, such as a Lisp symbol in
Emacs Lisp mode. For instance, if you perform an incremental symbol
search for the Lisp symbol forward-word, it would not match
isearch-forward-word. This feature is thus mainly useful for
searching source code.

Start a symbol incremental search forward with the symbol found near
point added to the search string initially.

M-s _ RETsymbolRET

Search forward for symbol, nonincrementally.

M-s _ C-r RETsymbolRET

Search backward for symbol, nonincrementally.

To begin a forward incremental symbol search, type M-s _ (or
M-s . if the symbol to search is near point). If incremental
search is not already active, this runs the command
isearch-forward-symbol. If incremental search is already
active, M-s _ switches to a symbol search, preserving the
direction of the search and the current search string; you can disable
symbol search by typing M-s _ again. In incremental symbol
search, only the beginning of the search string is required to match
the beginning of a symbol.

To begin a nonincremental symbol search, type M-s _ RET
for a forward search, or M-s _ C-r RET or a backward
search. In nonincremental symbol searches, the beginning and end of
the search string are required to match the beginning and end of a
symbol, respectively.

15.5 Regular Expression Search

A regular expression (or regexp for short) is a pattern
that denotes a class of alternative strings to match. Emacs
provides both incremental and nonincremental ways to search for a
match for a regexp. The syntax of regular expressions is explained in
the next section.

C-M-s

Begin incremental regexp search (isearch-forward-regexp).

C-M-r

Begin reverse incremental regexp search (isearch-backward-regexp).

Incremental search for a regexp is done by typing C-M-s
(isearch-forward-regexp), by invoking C-s with a
prefix argument (whose value does not matter), or by typing M-r
within a forward incremental search. This command reads a
search string incrementally just like C-s, but it treats the
search string as a regexp rather than looking for an exact match
against the text in the buffer. Each time you add text to the search
string, you make the regexp longer, and the new regexp is searched
for. To search backward for a regexp, use C-M-r
(isearch-backward-regexp), C-r with a prefix argument,
or M-r within a backward incremental search.

All of the special key sequences in an ordinary incremental search
do similar things in an incremental regexp search. For instance,
typing C-s immediately after starting the search retrieves the
last incremental search regexp used and searches forward for it.
Incremental regexp and non-regexp searches have independent defaults.
They also have separate search rings, which you can access with
M-p and M-n.

Unlike ordinary incremental search, incremental regexp search
do not use lax space matching by default. To toggle this feature
use M-s SPC (isearch-toggle-lax-whitespace).
Then any SPC typed in incremental regexp search will match
any sequence of one or more whitespace characters. The variable
search-whitespace-regexp specifies the regexp for the lax
space matching. See Special Isearch.

In some cases, adding characters to the regexp in an incremental
regexp search can make the cursor move back and start again. For
example, if you have searched for ‘foo’ and you add ‘\|bar’,
the cursor backs up in case the first ‘bar’ precedes the first
‘foo’. See Regexps.

Forward and backward regexp search are not symmetrical, because
regexp matching in Emacs always operates forward, starting with the
beginning of the regexp. Thus, forward regexp search scans forward,
trying a forward match at each possible starting position. Backward
regexp search scans backward, trying a forward match at each possible
starting position. These search methods are not mirror images.

Nonincremental search for a regexp is done with the commands
re-search-forward and re-search-backward. You can
invoke these with M-x, or by way of incremental regexp search
with C-M-s RET and C-M-r RET.

If you use the incremental regexp search commands with a prefix
argument, they perform ordinary string search, like
isearch-forward and isearch-backward. See Incremental Search.

15.6 Syntax of Regular Expressions

This manual describes regular expression features that users
typically use. See Regular Expressions in The Emacs Lisp
Reference Manual, for additional features used mainly in Lisp
programs.

Regular expressions have a syntax in which a few characters are
special constructs and the rest are ordinary. An ordinary
character matches that same character and nothing else. The special
characters are ‘$^.*+?[\’. The character ‘]’ is special if
it ends a character alternative (see later). The character ‘-’
is special inside a character alternative. Any other character
appearing in a regular expression is ordinary, unless a ‘\’
precedes it. (When you use regular expressions in a Lisp program,
each ‘\’ must be doubled, see the example near the end of this
section.)

For example, ‘f’ is not a special character, so it is ordinary, and
therefore ‘f’ is a regular expression that matches the string
‘f’ and no other string. (It does not match the string
‘ff’.) Likewise, ‘o’ is a regular expression that matches
only ‘o’. (When case distinctions are being ignored, these regexps
also match ‘F’ and ‘O’, but we consider this a generalization
of “the same string”, rather than an exception.)

Any two regular expressions a and b can be concatenated.
The result is a regular expression which matches a string if a
matches some amount of the beginning of that string and b
matches the rest of the string. For example, concatenating the
regular expressions ‘f’ and ‘o’ gives the regular expression
‘fo’, which matches only the string ‘fo’. Still trivial.
To do something nontrivial, you need to use one of the special
characters. Here is a list of them.

.(Period)

is a special character that matches any single character except a
newline. For example, the regular expressions ‘a.b’ matches any
three-character string that begins with ‘a’ and ends with
‘b’.

*

is not a construct by itself; it is a postfix operator that means to
match the preceding regular expression repetitively any number of
times, as many times as possible. Thus, ‘o*’ matches any number
of ‘o’s, including no ‘o’s.

‘*’ always applies to the smallest possible preceding
expression. Thus, ‘fo*’ has a repeating ‘o’, not a repeating
‘fo’. It matches ‘f’, ‘fo’, ‘foo’, and so on.

The matcher processes a ‘*’ construct by matching, immediately,
as many repetitions as can be found. Then it continues with the rest
of the pattern. If that fails, backtracking occurs, discarding some
of the matches of the ‘*’-modified construct in case that makes
it possible to match the rest of the pattern. For example, in matching
‘ca*ar’ against the string ‘caaar’, the ‘a*’ first
tries to match all three ‘a’s; but the rest of the pattern is
‘ar’ and there is only ‘r’ left to match, so this try fails.
The next alternative is for ‘a*’ to match only two ‘a’s.
With this choice, the rest of the regexp matches successfully.

+

is a postfix operator, similar to ‘*’ except that it must match
the preceding expression at least once. Thus, ‘ca+r’ matches the
strings ‘car’ and ‘caaaar’ but not the string ‘cr’,
whereas ‘ca*r’ matches all three strings.

?

is a postfix operator, similar to ‘*’ except that it can match
the preceding expression either once or not at all. Thus, ‘ca?r’
matches ‘car’ or ‘cr’, and nothing else.

*?, +?, ??

are non-greedy variants of the operators above. The normal
operators ‘*’, ‘+’, ‘?’ match as much as they can, as
long as the overall regexp can still match. With a following
‘?’, they will match as little as possible.

Thus, both ‘ab*’ and ‘ab*?’ can match the string ‘a’
and the string ‘abbbb’; but if you try to match them both against
the text ‘abbb’, ‘ab*’ will match it all (the longest valid
match), while ‘ab*?’ will match just ‘a’ (the shortest
valid match).

Non-greedy operators match the shortest possible string starting at a
given starting point; in a forward search, though, the earliest
possible starting point for match is always the one chosen. Thus, if
you search for ‘a.*?$’ against the text ‘abbab’ followed by
a newline, it matches the whole string. Since it can match
starting at the first ‘a’, it does.

\{n\}

is a postfix operator specifying n repetitions—that is, the
preceding regular expression must match exactly n times in a
row. For example, ‘x\{4\}’ matches the string ‘xxxx’ and
nothing else.

\{n,m\}

is a postfix operator specifying between n and m
repetitions—that is, the preceding regular expression must match at
least n times, but no more than m times. If m is
omitted, then there is no upper limit, but the preceding regular
expression must match at least n times. ‘\{0,1\}’ is
equivalent to ‘?’. ‘\{0,\}’ is equivalent to
‘*’. ‘\{1,\}’ is equivalent to ‘+’.

[ … ]

is a character set, beginning with ‘[’ and terminated by
‘]’.

In the simplest case, the characters between the two brackets are what
this set can match. Thus, ‘[ad]’ matches either one ‘a’ or
one ‘d’, and ‘[ad]*’ matches any string composed of just
‘a’s and ‘d’s (including the empty string). It follows that
‘c[ad]*r’ matches ‘cr’, ‘car’, ‘cdr’,
‘caddaar’, etc.

You can also include character ranges in a character set, by writing the
starting and ending characters with a ‘-’ between them. Thus,
‘[a-z]’ matches any lower-case ASCII letter. Ranges may be
intermixed freely with individual characters, as in ‘[a-z$%.]’,
which matches any lower-case ASCII letter or ‘$’, ‘%’ or
period.

You can also include certain special character classes in a
character set. A ‘[:’ and balancing ‘:]’ enclose a
character class inside a character alternative. For instance,
‘[[:alnum:]]’ matches any letter or digit. See Char Classes in The Emacs Lisp Reference Manual, for a list of character
classes.

To include a ‘]’ in a character set, you must make it the first
character. For example, ‘[]a]’ matches ‘]’ or ‘a’. To
include a ‘-’, write ‘-’ as the first or last character of the
set, or put it after a range. Thus, ‘[]-]’ matches both ‘]’
and ‘-’.

To include ‘^’ in a set, put it anywhere but at the beginning of
the set. (At the beginning, it complements the set—see below.)

When you use a range in case-insensitive search, you should write both
ends of the range in upper case, or both in lower case, or both should
be non-letters. The behavior of a mixed-case range such as ‘A-z’
is somewhat ill-defined, and it may change in future Emacs versions.

[^ … ]

‘[^’ begins a complemented character set, which matches any
character except the ones specified. Thus, ‘[^a-z0-9A-Z]’ matches
all characters exceptASCII letters and digits.

‘^’ is not special in a character set unless it is the first
character. The character following the ‘^’ is treated as if it
were first (in other words, ‘-’ and ‘]’ are not special there).

A complemented character set can match a newline, unless newline is
mentioned as one of the characters not to match. This is in contrast to
the handling of regexps in programs such as grep.

^

is a special character that matches the empty string, but only at the
beginning of a line in the text being matched. Otherwise it fails to
match anything. Thus, ‘^foo’ matches a ‘foo’ that occurs at
the beginning of a line.

For historical compatibility reasons, ‘^’ can be used with this
meaning only at the beginning of the regular expression, or after
‘\(’ or ‘\|’.

$

is similar to ‘^’ but matches only at the end of a line. Thus,
‘x+$’ matches a string of one ‘x’ or more at the end of a line.

For historical compatibility reasons, ‘$’ can be used with this
meaning only at the end of the regular expression, or before ‘\)’
or ‘\|’.

\

has two functions: it quotes the special characters (including
‘\’), and it introduces additional special constructs.

Because ‘\’ quotes special characters, ‘\$’ is a regular
expression that matches only ‘$’, and ‘\[’ is a regular
expression that matches only ‘[’, and so on.

See the following section for the special constructs that begin
with ‘\’.

Note: for historical compatibility, special characters are treated as
ordinary ones if they are in contexts where their special meanings make no
sense. For example, ‘*foo’ treats ‘*’ as ordinary since there is
no preceding expression on which the ‘*’ can act. It is poor practice
to depend on this behavior; it is better to quote the special character anyway,
regardless of where it appears.

As a ‘\’ is not special inside a character alternative, it can
never remove the special meaning of ‘-’ or ‘]’. So you
should not quote these characters when they have no special meaning
either. This would not clarify anything, since backslashes can
legitimately precede these characters where they have special
meaning, as in ‘[^\]’ ("[^\\]" for Lisp string syntax),
which matches any single character except a backslash.

15.7 Backslash in Regular Expressions

For the most part, ‘\’ followed by any character matches only
that character. However, there are several exceptions: two-character
sequences starting with ‘\’ that have special meanings. The
second character in the sequence is always an ordinary character when
used on its own. Here is a table of ‘\’ constructs.

\|

specifies an alternative. Two regular expressions a and b
with ‘\|’ in between form an expression that matches some text if
either a matches it or b matches it. It works by trying to
match a, and if that fails, by trying to match b.

Thus, ‘foo\|bar’ matches either ‘foo’ or ‘bar’
but no other string.

‘\|’ applies to the largest possible surrounding expressions. Only a
surrounding ‘\( … \)’ grouping can limit the grouping power of
‘\|’.

Full backtracking capability exists to handle multiple uses of ‘\|’.

\( … \)

is a grouping construct that serves three purposes:

To enclose a set of ‘\|’ alternatives for other operations.
Thus, ‘\(foo\|bar\)x’ matches either ‘foox’ or ‘barx’.

To enclose a complicated expression for the postfix operators ‘*’,
‘+’ and ‘?’ to operate on. Thus, ‘ba\(na\)*’ matches
‘bananana’, etc., with any (zero or more) number of ‘na’
strings.

To record a matched substring for future reference.

This last application is not a consequence of the idea of a
parenthetical grouping; it is a separate feature that is assigned as a
second meaning to the same ‘\( … \)’ construct. In practice
there is usually no conflict between the two meanings; when there is
a conflict, you can use a “shy” group.

\(?: … \)

specifies a “shy” group that does not record the matched substring;
you can’t refer back to it with ‘\d’. This is useful
in mechanically combining regular expressions, so that you
can add groups for syntactic purposes without interfering with
the numbering of the groups that are meant to be referred to.

\d

matches the same text that matched the dth occurrence of a
‘\( … \)’ construct. This is called a back
reference.

After the end of a ‘\( … \)’ construct, the matcher remembers
the beginning and end of the text matched by that construct. Then,
later on in the regular expression, you can use ‘\’ followed by the
digit d to mean “match the same text matched the dth time
by the ‘\( … \)’ construct”.

The strings matching the first nine ‘\( … \)’ constructs
appearing in a regular expression are assigned numbers 1 through 9 in
the order that the open-parentheses appear in the regular expression.
So you can use ‘\1’ through ‘\9’ to refer to the text matched
by the corresponding ‘\( … \)’ constructs.

For example, ‘\(.*\)\1’ matches any newline-free string that is
composed of two identical halves. The ‘\(.*\)’ matches the first
half, which may be anything, but the ‘\1’ that follows must match
the same exact text.

If a particular ‘\( … \)’ construct matches more than once
(which can easily happen if it is followed by ‘*’), only the last
match is recorded.

\`

matches the empty string, but only at the beginning of the string or
buffer (or its accessible portion) being matched against.

\'

matches the empty string, but only at the end of the string or buffer
(or its accessible portion) being matched against.

\=

matches the empty string, but only at point.

\b

matches the empty string, but only at the beginning or
end of a word. Thus, ‘\bfoo\b’ matches any occurrence of
‘foo’ as a separate word. ‘\bballs?\b’ matches
‘ball’ or ‘balls’ as a separate word.

‘\b’ matches at the beginning or end of the buffer
regardless of what text appears next to it.

\B

matches the empty string, but not at the beginning or
end of a word.

\<

matches the empty string, but only at the beginning of a word.
‘\<’ matches at the beginning of the buffer only if a
word-constituent character follows.

\>

matches the empty string, but only at the end of a word. ‘\>’
matches at the end of the buffer only if the contents end with a
word-constituent character.

\w

matches any word-constituent character. The syntax table determines
which characters these are. See Syntax Tables in The Emacs Lisp Reference Manual.

\W

matches any character that is not a word-constituent.

\_<

matches the empty string, but only at the beginning of a symbol.
A symbol is a sequence of one or more symbol-constituent characters.
A symbol-constituent character is a character whose syntax is either
‘w’ or ‘_’. ‘\_<’ matches at the beginning of the
buffer only if a symbol-constituent character follows.

\_>

matches the empty string, but only at the end of a symbol. ‘\_>’
matches at the end of the buffer only if the contents end with a
symbol-constituent character.

\sc

matches any character whose syntax is c. Here c is a
character that designates a particular syntax class: thus, ‘w’
for word constituent, ‘-’ or ‘’ for whitespace, ‘.’
for ordinary punctuation, etc. See Syntax Tables in The Emacs Lisp Reference Manual.

\Sc

matches any character whose syntax is not c.

\cc

matches any character that belongs to the category c. For
example, ‘\cc’ matches Chinese characters, ‘\cg’ matches
Greek characters, etc. For the description of the known categories,
type M-x describe-categories RET.

\Cc

matches any character that does not belong to category
c.

The constructs that pertain to words and syntax are controlled by
the setting of the syntax table. See Syntax Tables in The Emacs Lisp Reference Manual.

15.9 Searching and Case

Searches in Emacs normally ignore the case of the text they are
searching through, if you specify the text in lower case. Thus, if
you specify searching for ‘foo’, then ‘Foo’ and ‘foo’
also match. Regexps, and in particular character sets, behave
likewise: ‘[ab]’ matches ‘a’ or ‘A’ or ‘b’ or
‘B’.

An upper-case letter anywhere in the incremental search string makes
the search case-sensitive. Thus, searching for ‘Foo’ does not find
‘foo’ or ‘FOO’. This applies to regular expression search as
well as to string search. The effect ceases if you delete the
upper-case letter from the search string.

If you set the variable case-fold-search to nil, then
all letters must match exactly, including case. This is a per-buffer
variable; altering the variable normally affects only the current buffer,
unless you change its default value. See Locals.
This variable applies to nonincremental searches also, including those
performed by the replace commands (see Replace) and the minibuffer
history matching commands (see Minibuffer History).

Typing M-c within an incremental search toggles the case
sensitivity of that search. The effect does not extend beyond the
current incremental search to the next one, but it does override the
effect of adding or removing an upper-case letter in the current
search.

Several related variables control case-sensitivity of searching and
matching for specific commands or activities. For instance,
tags-case-fold-search controls case sensitivity for
find-tag. To find these variables, do M-x
apropos-variable RET case-fold-search RET.

15.10 Replacement Commands

Emacs provides several commands for performing search-and-replace
operations. In addition to the simple M-x replace-string
command, there is M-% (query-replace), which presents
each occurrence of the pattern and asks you whether to replace it.

The replace commands normally operate on the text from point to the
end of the buffer. When the region is active, they operate on it
instead (see Mark). The basic replace commands replace one
search string (or regexp) with one replacement string. It
is possible to perform several replacements in parallel, using the
command expand-region-abbrevs (see Expanding Abbrevs).

Unlike incremental search, the replacement commands do not use lax
space matching (see Special Isearch) by default. To enable lax
space matching for replacement, change the variable
replace-lax-whitespace to t. (This only affects how
Emacs finds the text to replace, not the replacement text.)

15.10.1 Unconditional Replacement

M-x replace-string RETstringRETnewstringRET

Replace every occurrence of string with newstring.

To replace every instance of ‘foo’ after point with ‘bar’,
use the command M-x replace-string with the two arguments
‘foo’ and ‘bar’. Replacement happens only in the text after
point, so if you want to cover the whole buffer you must go to the
beginning first. All occurrences up to the end of the buffer are
replaced; to limit replacement to part of the buffer, activate the
region around that part. When the region is active, replacement is
limited to the region (see Mark).

When replace-string exits, it leaves point at the last
occurrence replaced. It adds the prior position of point (where the
replace-string command was issued) to the mark ring, without
activating the mark; use C-u C-SPC to move back there.
See Mark Ring.

A prefix argument restricts replacement to matches that are
surrounded by word boundaries.

15.10.2 Regexp Replacement

The M-x replace-string command replaces exact matches for a
single string. The similar command M-x replace-regexp replaces
any match for a specified pattern.

M-x replace-regexp RETregexpRETnewstringRET

Replace every match for regexp with newstring.

In replace-regexp, the newstring need not be constant:
it can refer to all or part of what is matched by the regexp.
‘\&’ in newstring stands for the entire match being
replaced. ‘\d’ in newstring, where d is a
digit, stands for whatever matched the dth parenthesized
grouping in regexp. (This is called a “back reference”.)
‘\#’ refers to the count of replacements already made in this
command, as a decimal number. In the first replacement, ‘\#’
stands for ‘0’; in the second, for ‘1’; and so on. For
example,

M-x replace-regexp RET c[ad]+r RET \&-safe RET

replaces (for example) ‘cadr’ with ‘cadr-safe’ and ‘cddr’
with ‘cddr-safe’.

M-x replace-regexp RET \(c[ad]+r\)-safe RET \1 RET

performs the inverse transformation. To include a ‘\’ in the
text to replace with, you must enter ‘\\’.

If you want to enter part of the replacement string by hand each
time, use ‘\?’ in the replacement string. Each replacement will
ask you to edit the replacement string in the minibuffer, putting
point where the ‘\?’ was.

The remainder of this subsection is intended for specialized tasks
and requires knowledge of Lisp. Most readers can skip it.

You can use Lisp expressions to calculate parts of the
replacement string. To do this, write ‘\,’ followed by the
expression in the replacement string. Each replacement calculates the
value of the expression and converts it to text without quoting (if
it’s a string, this means using the string’s contents), and uses it in
the replacement string in place of the expression itself. If the
expression is a symbol, one space in the replacement string after the
symbol name goes with the symbol name, so the value replaces them
both.

Inside such an expression, you can use some special sequences.
‘\&’ and ‘\n’ refer here, as usual, to the entire
match as a string, and to a submatch as a string. n may be
multiple digits, and the value of ‘\n’ is nil if
subexpression n did not match. You can also use ‘\#&’ and
‘\#n’ to refer to those matches as numbers (this is valid
when the match or submatch has the form of a numeral). ‘\#’ here
too stands for the number of already-completed replacements.

Repeating our example to exchange ‘x’ and ‘y’, we can thus
do it also this way:

M-x replace-regexp RET \(x\)\|y RET
\,(if \1 "y" "x") RET

For computing replacement strings for ‘\,’, the format
function is often useful (see Formatting Strings in The Emacs
Lisp Reference Manual). For example, to add consecutively numbered
strings like ‘ABC00042’ to columns 73 to 80 (unless they are
already occupied), you can use

15.10.3 Replace Commands and Case

If the first argument of a replace command is all lower case, the
command ignores case while searching for occurrences to
replace—provided case-fold-search is non-nil. If
case-fold-search is set to nil, case is always significant
in all searches.

In addition, when the newstring argument is all or partly lower
case, replacement commands try to preserve the case pattern of each
occurrence. Thus, the command

M-x replace-string RET foo RET bar RET

replaces a lower case ‘foo’ with a lower case ‘bar’, an
all-caps ‘FOO’ with ‘BAR’, and a capitalized ‘Foo’ with
‘Bar’. (These three alternatives—lower case, all caps, and
capitalized, are the only ones that replace-string can
distinguish.)

If upper-case letters are used in the replacement string, they remain
upper case every time that text is inserted. If upper-case letters are
used in the first argument, the second argument is always substituted
exactly as given, with no case conversion. Likewise, if either
case-replace or case-fold-search is set to nil,
replacement is done without case conversion.

15.10.4 Query Replace

M-% stringRETnewstringRET

Replace some occurrences of string with newstring.

C-M-% regexpRETnewstringRET

Replace some matches for regexp with newstring.

If you want to change only some of the occurrences of ‘foo’ to
‘bar’, not all of them, use M-% (query-replace).
This command finds occurrences of ‘foo’ one by one, displays each
occurrence and asks you whether to replace it. Aside from querying,
query-replace works just like replace-string
(see Unconditional Replace). In particular, it preserves case
provided case-replace is non-nil, as it normally is
(see Replacement and Case). A numeric argument means to consider
only occurrences that are bounded by word-delimiter characters. A
negative prefix argument replaces backward.

C-M-% performs regexp search and replace (query-replace-regexp).
It works like replace-regexp except that it queries
like query-replace.

These commands highlight the current match using the face
query-replace. They highlight other matches using
lazy-highlight just like incremental search (see Incremental Search). By default, query-replace-regexp will show the
substituted replacement string for the current match in the
minibuffer. If you want to keep special sequences ‘\&’ and
‘\n’ unexpanded, customize
query-replace-show-replacement variable.

The characters you can type when you are shown a match for the string
or regexp are:

SPC

to replace the occurrence with newstring.

DEL

to skip to the next occurrence without replacing this one.

, (Comma)

to replace this occurrence and display the result. You are then asked
for another input character to say what to do next. Since the
replacement has already been made, DEL and SPC are
equivalent in this situation; both move to the next occurrence.

You can type C-r at this point (see below) to alter the replaced
text. You can also type C-x u to undo the replacement; this exits
the query-replace, so if you want to do further replacement you
must use C-x ESCESCRET to restart
(see Repetition).

RET

to exit without doing any more replacements.

. (Period)

to replace this occurrence and then exit without searching for more
occurrences.

!

to replace all remaining occurrences without asking again.

Y (Upper-case)

to replace all remaining occurrences in all remaining buffers in
multi-buffer replacements (like the Dired Q command that performs
query replace on selected files). It answers this question and all
subsequent questions in the series with "yes", without further
user interaction.

N (Upper-case)

to skip to the next buffer in multi-buffer replacements without
replacing remaining occurrences in the current buffer. It answers
this question "no", gives up on the questions for the current buffer,
and continues to the next buffer in the sequence.

^

to go back to the position of the previous occurrence (or what used to
be an occurrence), in case you changed it by mistake or want to
reexamine it.

C-r

to enter a recursive editing level, in case the occurrence needs to be
edited rather than just replaced with newstring. When you are
done, exit the recursive editing level with C-M-c to proceed to
the next occurrence. See Recursive Edit.

C-w

to delete the occurrence, and then enter a recursive editing level as in
C-r. Use the recursive edit to insert text to replace the deleted
occurrence of string. When done, exit the recursive editing level
with C-M-c to proceed to the next occurrence.

e

to edit the replacement string in the minibuffer. When you exit the
minibuffer by typing RET, the minibuffer contents replace the
current occurrence of the pattern. They also become the new
replacement string for any further occurrences.

C-l

to redisplay the screen. Then you must type another character to
specify what to do with this occurrence.

C-h

to display a message summarizing these options. Then you must type
another character to specify what to do with this occurrence.

Some other characters are aliases for the ones listed above: y,
n and q are equivalent to SPC, DEL and
RET.

Aside from this, any other character exits the query-replace,
and is then reread as part of a key sequence. Thus, if you type
C-k, it exits the query-replace and then kills to end of
line.

To restart a query-replace once it is exited, use C-x
ESCESC, which repeats the query-replace because it
used the minibuffer to read its arguments. See C-x ESC
ESC.

See Operating on Files, for the Dired Q command which
performs query replace on selected files. See also Transforming File Names, for Dired commands to rename, copy, or link files by
replacing regexp matches in file names.

15.11 Other Search-and-Loop Commands

Here are some other commands that find matches for a regular
expression. They all ignore case in matching, if the pattern contains
no upper-case letters and case-fold-search is non-nil.
Aside from occur and its variants, all operate on the text from
point to the end of the buffer, or on the region if it is active.

M-x multi-isearch-buffers

Prompt for one or more buffer names, ending with RET; then,
begin a multi-buffer incremental search in those buffers. (If the
search fails in one buffer, the next C-s tries searching the
next specified buffer, and so forth.) With a prefix argument, prompt
for a regexp and begin a multi-buffer incremental search in buffers
matching that regexp.

M-x multi-isearch-buffers-regexp

This command is just like multi-isearch-buffers, except it
performs an incremental regexp search.

M-x occur

Prompt for a regexp, and display a list showing each line in the
buffer that contains a match for it. To limit the search to part of
the buffer, narrow to that part (see Narrowing). A numeric
argument n specifies that n lines of context are to be
displayed before and after each matching line.

In the *Occur* buffer, you can click on each entry, or move
point there and type RET, to visit the corresponding position in
the buffer that was searched. o and C-o display the match
in another window; C-o does not select it. Alternatively, you
can use the C-x ` (next-error) command to visit the
occurrences one by one (see Compilation Mode).

Typing e in the *Occur* buffer switches to Occur Edit
mode, in which edits made to the entries are also applied to the text
in the originating buffer. Type C-c C-c to return to Occur
mode.

The command M-x list-matching-lines is a synonym for M-x
occur.

M-s o

Run occur using the search string of the last incremental
string search. You can also run M-s o when an incremental
search is active; this uses the current search string.

M-x multi-occur

This command is just like occur, except it is able to search
through multiple buffers. It asks you to specify the buffer names one
by one.

M-x multi-occur-in-matching-buffers

This command is similar to multi-occur, except the buffers to
search are specified by a regular expression that matches visited file
names. With a prefix argument, it uses the regular expression to
match buffer names instead.

M-x how-many

Prompt for a regexp, and print the number of matches for it in the
buffer after point. If the region is active, this operates on the
region instead.

M-x flush-lines

Prompt for a regexp, and delete each line that contains a match for
it, operating on the text after point. This command deletes the
current line if it contains a match starting after point. If the
region is active, it operates on the region instead; if a line
partially contained in the region contains a match entirely contained
in the region, it is deleted.

If a match is split across lines, flush-lines deletes all those
lines. It deletes the lines before starting to look for the next
match; hence, it ignores a match starting on the same line at which
another match ended.

M-x keep-lines

Prompt for a regexp, and delete each line that does not contain
a match for it, operating on the text after point. If point is not at
the beginning of a line, this command always keeps the current line.
If the region is active, the command operates on the region instead;
it never deletes lines that are only partially contained in the region
(a newline that ends a line counts as part of that line).

16 Commands for Fixing Typos

In this chapter we describe commands that are useful when you catch
a mistake while editing. The most fundamental of these commands is
the undo command C-/ (also bound to C-x u and C-_).
This undoes a single command, or a
part of a command (as in the case of query-replace), or several
consecutive character insertions. Consecutive repetitions of
C-/ undo earlier and earlier changes, back to the limit of the
undo information available.

Aside from the commands described here, you can erase text using
deletion commands such as DEL (delete-backward-char).
These were described earlier in this manual. See Erasing.

16.1 Undo

The undo command reverses recent changes in the buffer’s text.
Each buffer records changes individually, and the undo command always
applies to the current buffer. You can undo all the changes in a
buffer for as far back as the buffer’s records go. Usually, each editing
command makes a separate entry in the undo records, but some commands
such as query-replace divide their changes into multiple
entries for flexibility in undoing. Consecutive character insertion
commands are usually grouped together into a single undo record, to
make undoing less tedious.

C-/

C-x u

C-_

Undo one entry in the current buffer’s undo records (undo).

To begin to undo, type C-/ (or its aliases, C-_ or
C-x u)6. This undoes the most recent change in the buffer,
and moves point back to where it was before that change.
Consecutive repetitions of C-/ (or its aliases) undo earlier
and earlier changes in the current buffer. If all the recorded
changes have already been undone, the undo command signals an error.

Any command other than an undo command breaks the sequence of undo
commands. Starting from that moment, the entire sequence of undo
commands that you have just performed are themselves placed into the
undo record, as a single set of changes. Therefore, to re-apply
changes you have undone, type C-f or any other command that
harmlessly breaks the sequence of undoing; then type C-/ to undo
the undo command.

Alternatively, if you want to resume undoing, without redoing
previous undo commands, use M-x undo-only. This is like
undo, but will not redo changes you have just undone.

If you notice that a buffer has been modified accidentally, the
easiest way to recover is to type C-/ repeatedly until the stars
disappear from the front of the mode line (see Mode Line).
Whenever an undo command makes the stars disappear from the mode line,
it means that the buffer contents are the same as they were when the
file was last read in or saved. If you do not remember whether you
changed the buffer deliberately, type C-/ once. When you see
the last change you made undone, you will see whether it was an
intentional change. If it was an accident, leave it undone. If it
was deliberate, redo the change as described above.

When there is an active region, any use of undo performs
selective undo: it undoes the most recent change within the
region, instead of the entire buffer. However, when Transient Mark
mode is off (see Disabled Transient Mark), C-/ always
operates on the entire buffer, ignoring the region. In this case, you
can perform selective undo by supplying a prefix argument to the
undo command: C-u C-/. To undo further changes in the
same region, repeat the undo command (no prefix argument is
needed).

Some specialized buffers do not make undo records. Buffers whose
names start with spaces never do; these buffers are used internally by
Emacs to hold text that users don’t normally look at or edit.

When the undo information for a buffer becomes too large, Emacs discards
the oldest records from time to time (during garbage
collection). You can specify how much undo information to keep by
setting the variables undo-limit, undo-strong-limit, and
undo-outer-limit. Their values are expressed in bytes.

The variable undo-limit sets a soft limit: Emacs keeps undo
data for enough commands to reach this size, and perhaps exceed it,
but does not keep data for any earlier commands beyond that. Its
default value is 80000. The variable undo-strong-limit sets a
stricter limit: any previous command (though not the most recent one)
that pushes the size past this amount is forgotten. The default value
of undo-strong-limit is 120000.

Regardless of the values of those variables, the most recent change
is never discarded unless it gets bigger than undo-outer-limit
(normally 12,000,000). At that point, Emacs discards the undo data and
warns you about it. This is the only situation in which you cannot
undo the last command. If this happens, you can increase the value of
undo-outer-limit to make it even less likely to happen in the
future. But if you didn’t expect the command to create such large
undo data, then it is probably a bug and you should report it.
See Reporting Bugs.

16.2 Transposing Text

C-t

Transpose two characters (transpose-chars).

M-t

Transpose two words (transpose-words).

C-M-t

Transpose two balanced expressions (transpose-sexps).

C-x C-t

Transpose two lines (transpose-lines).

The common error of transposing two characters can be fixed, when they
are adjacent, with the C-t command (transpose-chars). Normally,
C-t transposes the two characters on either side of point. When
given at the end of a line, rather than transposing the last character of
the line with the newline, which would be useless, C-t transposes the
last two characters on the line. So, if you catch your transposition error
right away, you can fix it with just a C-t. If you don’t catch it so
fast, you must move the cursor back between the two transposed
characters before you type C-t. If you transposed a space with
the last character of the word before it, the word motion commands are
a good way of getting there. Otherwise, a reverse search (C-r)
is often the best way. See Search.

M-t transposes the word before point with the word after point
(transpose-words). It moves point forward over a word,
dragging the word preceding or containing point forward as well. The
punctuation characters between the words do not move. For example,
‘FOO, BAR’ transposes into ‘BAR, FOO’ rather than
‘BAR FOO,’.

C-M-t (transpose-sexps) is a similar command for
transposing two expressions (see Expressions), and C-x C-t
(transpose-lines) exchanges lines. They work like M-t
except as regards what units of text they transpose.

A numeric argument to a transpose command serves as a repeat count: it
tells the transpose command to move the character (word, expression, line)
before or containing point across several other characters (words,
expressions, lines). For example, C-u 3 C-t moves the character before
point forward across three other characters. It would change
‘f∗oobar’ into ‘oobf∗ar’. This is equivalent to
repeating C-t three times. C-u - 4 M-t moves the word
before point backward across four words. C-u - C-M-t would cancel
the effect of plain C-M-t.

A numeric argument of zero is assigned a special meaning (because
otherwise a command with a repeat count of zero would do nothing): to
transpose the character (word, expression, line) ending after point
with the one ending after the mark.

16.3 Case Conversion

M-- M-l

Convert last word to lower case. Note Meta-- is Meta-minus.

M-- M-u

Convert last word to all upper case.

M-- M-c

Convert last word to lower case with capital initial.

A very common error is to type words in the wrong case. Because of this,
the word case-conversion commands M-l, M-u and M-c have a
special feature when used with a negative argument: they do not move the
cursor. As soon as you see you have mistyped the last word, you can simply
case-convert it and go on typing. See Case.

16.4 Checking and Correcting Spelling

This section describes the commands to check the spelling of a
single word or of a portion of a buffer. These commands only work if
the spelling checker program Aspell, Ispell or Hunspell is installed.
These programs are not part of Emacs, but one of them is usually
installed in GNU/Linux and other free operating systems.
See Aspell in The Aspell Manual.

M-$

Check and correct spelling of the word at point (ispell-word).
If the region is active, do it for all words in the region instead.

M-x ispell

Check and correct spelling of all words in the buffer. If the region
is active, do it for all words in the region instead.

Restart the Aspell/Ispell/Hunspell process, using dict as the dictionary.

M-x ispell-kill-ispell

Kill the Aspell/Ispell/Hunspell subprocess.

M-TAB

ESCTAB

Complete the word before point based on the spelling dictionary
(ispell-complete-word).

M-x flyspell-mode

Enable Flyspell mode, which highlights all misspelled words.

M-x flyspell-prog-mode

Enable Flyspell mode for comments and strings only.

To check the spelling of the word around or before point, and
optionally correct it as well, type M-$ (ispell-word).
If a region is active, M-$ checks the spelling of all words
within the region. See Mark. (When Transient Mark mode is off,
M-$ always acts on the word around or before point, ignoring the
region; see Disabled Transient Mark.)

Similarly, the command M-x ispell performs spell-checking in
the region if one is active, or in the entire buffer otherwise. The
commands M-x ispell-buffer and M-x ispell-region
explicitly perform spell-checking on the entire buffer or the region
respectively. To check spelling in an email message you are writing,
use M-x ispell-message; that command checks the whole buffer,
except for material that is indented or appears to be cited from other
messages. See Sending Mail.

When one of these commands encounters what appears to be an
incorrect word, it asks you what to do. It usually displays a list of
numbered “near-misses”—words that are close to the incorrect word.
Then you must type a single-character response. Here are the valid
responses:

digit

Replace the word, just this time, with one of the displayed
near-misses. Each near-miss is listed with a digit; type that digit
to select it.

SPC

Skip this word—continue to consider it incorrect, but don’t change it
here.

r newRET

Replace the word, just this time, with new. (The replacement
string will be rescanned for more spelling errors.)

R newRET

Replace the word with new, and do a query-replace so you
can replace it elsewhere in the buffer if you wish. (The replacements
will be rescanned for more spelling errors.)

a

Accept the incorrect word—treat it as correct, but only in this
editing session.

A

Accept the incorrect word—treat it as correct, but only in this
editing session and for this buffer.

i

Insert this word in your private dictionary file so that Aspell or Ispell
or Hunspell will consider it correct from now on, even in future sessions.

m

Like i, but you can also specify dictionary completion
information.

u

Insert the lower-case version of this word in your private dictionary
file.

l wordRET

Look in the dictionary for words that match word. These words
become the new list of “near-misses”; you can select one of them as
the replacement by typing a digit. You can use ‘*’ in word as a
wildcard.

C-g

X

Quit interactive spell checking, leaving point at the word that was
being checked. You can restart checking again afterward with C-u
M-$.

x

Quit interactive spell checking and move point back to where it was
when you started spell checking.

In Text mode and related modes, M-TAB
(ispell-complete-word) performs in-buffer completion based on
spelling correction. Insert the beginning of a word, and then type
M-TAB; this shows a list of completions. (If your
window manager intercepts M-TAB, type ESCTAB or C-M-i.) Each completion is listed with a digit or
character; type that digit or character to choose it.

Once started, the Aspell or Ispell or Hunspell subprocess continues
to run, waiting for something to do, so that subsequent spell checking
commands complete more quickly. If you want to get rid of the
process, use M-x ispell-kill-ispell. This is not usually
necessary, since the process uses no processor time except when you do
spelling correction.

Ispell, Aspell and Hunspell look up spelling in two dictionaries:
the standard dictionary and your personal dictionary. The standard
dictionary is specified by the variable ispell-local-dictionary
or, if that is nil, by the variable ispell-dictionary.
If both are nil, the spelling program’s default dictionary is
used. The command M-x ispell-change-dictionary sets the
standard dictionary for the buffer and then restarts the subprocess,
so that it will use a different standard dictionary. Your personal
dictionary is specified by the variable
ispell-personal-dictionary. If that is nil, the
spelling program looks for a personal dictionary in a default
location.

A separate dictionary is used for word completion. The variable
ispell-complete-word-dict specifies the file name of this
dictionary. The completion dictionary must be different because it
cannot use root and affix information. For some languages, there
is a spell checking dictionary but no word completion dictionary.

Flyspell mode is a minor mode that performs automatic spell checking
as you type. When it finds a word that it does not recognize, it
highlights that word. Type M-x flyspell-mode to toggle Flyspell
mode in the current buffer. To enable Flyspell mode in all text mode
buffers, add flyspell-mode to text-mode-hook.
See Hooks.

When Flyspell mode highlights a word as misspelled, you can click on
it with Mouse-2 to display a menu of possible corrections and
actions. You can also correct the word by editing it manually in any
way you like.

Flyspell Prog mode works just like ordinary Flyspell mode, except
that it only checks words in comments and string constants. This
feature is useful for editing programs. Type M-x
flyspell-prog-mode to enable or disable this mode in the current
buffer. To enable this mode in all programming mode buffers, add
flyspell-prog-mode to prog-mode-hook (see Hooks).

17 Keyboard Macros

In this chapter we describe how to record a sequence of editing
commands so you can repeat it conveniently later.

A keyboard macro is a command defined by an Emacs user to stand for
another sequence of keys. For example, if you discover that you are
about to type C-n M-d C-d forty times, you can speed your work by
defining a keyboard macro to do C-n M-d C-d, and then executing
it 39 more times.

You define a keyboard macro by executing and recording the commands
which are its definition. Put differently, as you define a keyboard
macro, the definition is being executed for the first time. This way,
you can see the effects of your commands, so that you don’t have to
figure them out in your head. When you close the definition, the
keyboard macro is defined and also has been, in effect, executed once.
You can then do the whole thing over again by invoking the macro.

Keyboard macros differ from ordinary Emacs commands in that they are
written in the Emacs command language rather than in Lisp. This makes it
easier for the novice to write them, and makes them more convenient as
temporary hacks. However, the Emacs command language is not powerful
enough as a programming language to be useful for writing anything
intelligent or general. For such things, Lisp must be used.

17.1 Basic Use

If a keyboard macro is being defined, end the definition; otherwise,
execute the most recent keyboard macro
(kmacro-end-or-call-macro).

C-u F3

Re-execute last keyboard macro, then append keys to its definition.

C-u C-u F3

Append keys to the last keyboard macro without re-executing it.

C-x C-k r

Run the last keyboard macro on each line that begins in the region
(apply-macro-to-region-lines).

To start defining a keyboard macro, type F3. From then on,
your keys continue to be executed, but also become part of the
definition of the macro. ‘Def’ appears in the mode line to
remind you of what is going on. When you are finished, type F4
(kmacro-end-or-call-macro) to terminate the definition. For
example,

F3 M-f foo F4

defines a macro to move forward a word and then insert ‘foo’.
Note that F3 and F4 do not become part of the macro.

After defining the macro, you can call it with F4. For the
above example, this has the same effect as typing M-f foo again.
(Note the two roles of the F4 command: it ends the macro if you
are in the process of defining one, or calls the last macro
otherwise.) You can also supply F4 with a numeric prefix
argument ‘n’, which means to invoke the macro ‘n’ times. An
argument of zero repeats the macro indefinitely, until it gets an
error or you type C-g (or, on MS-DOS, C-BREAK).

The above example demonstrates a handy trick that you can employ
with keyboard macros: if you wish to repeat an operation at regularly
spaced places in the text, include a motion command as part of the
macro. In this case, repeating the macro inserts the string
‘foo’ after each successive word.

After terminating the definition of a keyboard macro, you can append
more keystrokes to its definition by typing C-u F3. This
is equivalent to plain F3 followed by retyping the whole
definition so far. As a consequence, it re-executes the macro as
previously defined. If you change the variable
kmacro-execute-before-append to nil, the existing macro
will not be re-executed before appending to it (the default is
t). You can also add to the end of the definition of the last
keyboard macro without re-executing it by typing C-u C-u
F3.

When a command reads an argument with the minibuffer, your
minibuffer input becomes part of the macro along with the command. So
when you replay the macro, the command gets the same argument as when
you entered the macro. For example,

F3 C-a C-k C-x b foo RET C-y C-x b RETF4

defines a macro that kills the current line, yanks it into the buffer
‘foo’, then returns to the original buffer.

Most keyboard commands work as usual in a keyboard macro definition,
with some exceptions. Typing C-g (keyboard-quit) quits
the keyboard macro definition. Typing C-M-c
(exit-recursive-edit) can be unreliable: it works as you’d
expect if exiting a recursive edit that started within the macro, but
if it exits a recursive edit that started before you invoked the
keyboard macro, it also necessarily exits the keyboard macro too.
Mouse events are also unreliable, even though you can use them in a
keyboard macro: when the macro replays the mouse event, it uses the
original mouse position of that event, the position that the mouse had
while you were defining the macro. The effect of this may be hard to
predict.

The command C-x C-k r (apply-macro-to-region-lines)
repeats the last defined keyboard macro on each line that begins in
the region. It does this line by line, by moving point to the
beginning of the line and then executing the macro.

In addition to the F3 and F4 commands described above,
Emacs also supports an older set of key bindings for defining and
executing keyboard macros. To begin a macro definition, type C-x
( (kmacro-start-macro); as with F3, a prefix argument
appends this definition to the last keyboard macro. To end a macro
definition, type C-x ) (kmacro-end-macro). To execute
the most recent macro, type C-x e
(kmacro-end-and-call-macro). If you enter C-x e while
defining a macro, the macro is terminated and executed immediately.
Immediately after typing C-x e, you can type e repeatedly
to immediately repeat the macro one or more times. You can also give
C-x e a repeat argument, just like F4.

C-x ) can be given a repeat count as an argument. This means
to repeat the macro right after defining it. The macro definition
itself counts as the first repetition, since it is executed as you
define it, so C-u 4 C-x ) executes the macro immediately 3
additional times.

All commands which operate on the keyboard macro ring use the
same C-x C-k prefix. Most of these commands can be executed and
repeated immediately after each other without repeating the C-x
C-k prefix. For example,

C-x C-k C-p C-p C-k C-k C-k C-n C-n C-k C-p C-k C-d

will rotate the keyboard macro ring to the “second previous” macro,
execute the resulting head macro three times, rotate back to the
original head macro, execute that once, rotate to the “previous”
macro, execute that, and finally delete it from the macro ring.

The command C-x C-k C-k (kmacro-end-or-call-macro-repeat)
executes the keyboard macro at the head of the macro ring. You can
repeat the macro immediately by typing another C-k, or you can
rotate the macro ring immediately by typing C-n or C-p.

When a keyboard macro is being defined, C-x C-k C-k behaves
like F4 except that, immediately afterward, you can use most key
bindings of this section without the C-x C-k prefix. For
instance, another C-k will re-execute the macro.

The commands C-x C-k C-n (kmacro-cycle-ring-next) and
C-x C-k C-p (kmacro-cycle-ring-previous) rotate the
macro ring, bringing the next or previous keyboard macro to the head
of the macro ring. The definition of the new head macro is displayed
in the echo area. You can continue to rotate the macro ring
immediately by repeating just C-n and C-p until the
desired macro is at the head of the ring. To execute the new macro
ring head immediately, just type C-k.

Note that Emacs treats the head of the macro ring as the “last
defined keyboard macro”. For instance, F4 will execute that
macro, and C-x C-k n will give it a name.

The maximum number of macros stored in the keyboard macro ring is
determined by the customizable variable kmacro-ring-max.

17.3 The Keyboard Macro Counter

Each keyboard macro has an associated counter, which is initialized
to 0 when you start defining the macro. This counter allows you to
insert a number into the buffer that depends on the number of times
the macro has been called. The counter is incremented each time its
value is inserted into the buffer.

F3

In a keyboard macro definition, insert the keyboard macro counter
value in the buffer (kmacro-start-macro-or-insert-counter).

C-x C-k C-i

Insert the keyboard macro counter value in the buffer
(kmacro-insert-counter).

C-x C-k C-c

Set the keyboard macro counter (kmacro-set-counter).

C-x C-k C-a

Add the prefix arg to the keyboard macro counter (kmacro-add-counter).

C-x C-k C-f

Specify the format for inserting the keyboard macro counter
(kmacro-set-format).

When you are defining a keyboard macro, the command F3
(kmacro-start-macro-or-insert-counter) inserts the current
value of the keyboard macro’s counter into the buffer, and increments
the counter by 1. (If you are not defining a macro, F3 begins a
macro definition instead. See Basic Keyboard Macro.) You can use
a numeric prefix argument to specify a different increment. If you
just specify a C-u prefix, that is the same as an increment of
zero: it inserts the current counter value without changing it.

As an example, let us show how the keyboard macro counter can be
used to build a numbered list. Consider the following key sequence:

F3 C-a F3 . SPCF4

As part of this keyboard macro definition, the string ‘0. ’ was
inserted into the beginning of the current line. If you now move
somewhere else in the buffer and type F4 to invoke the macro,
the string ‘1. ’ is inserted at the beginning of that line.
Subsequent invocations insert ‘2. ’, ‘3. ’, and so forth.

The command C-x C-k C-i (kmacro-insert-counter) does
the same thing as F3, but it can be used outside a keyboard
macro definition. When no keyboard macro is being defined or
executed, it inserts and increments the counter of the macro at the
head of the keyboard macro ring.

The command C-x C-k C-c (kmacro-set-counter) sets the
current macro counter to the value of the numeric argument. If you use
it inside the macro, it operates on each repetition of the macro. If
you specify just C-u as the prefix, while executing the macro,
that resets the counter to the value it had at the beginning of the
current repetition of the macro (undoing any increments so far in this
repetition).

The command C-x C-k C-a (kmacro-add-counter) adds the
prefix argument to the current macro counter. With just C-u as
argument, it resets the counter to the last value inserted by any
keyboard macro. (Normally, when you use this, the last insertion
will be in the same macro and it will be the same counter.)

The command C-x C-k C-f (kmacro-set-format) prompts for
the format to use when inserting the macro counter. The default
format is ‘%d’, which means to insert the number in decimal
without any padding. You can exit with empty minibuffer to reset the
format to this default. You can specify any format string that the
format function accepts and that makes sense with a single
integer extra argument (see Formatting Strings in The Emacs
Lisp Reference Manual). Do not put the format string inside double
quotes when you insert it in the minibuffer.

If you use this command while no keyboard macro is being defined or
executed, the new format affects all subsequent macro definitions.
Existing macros continue to use the format in effect when they were
defined. If you set the format while defining a keyboard macro, this
affects the macro being defined from that point on, but it does not
affect subsequent macros. Execution of the macro will, at each step,
use the format in effect at that step during its definition. Changes
to the macro format during execution of a macro, like the
corresponding changes during its definition, have no effect on
subsequent macros.

The format set by C-x C-k C-f does not affect insertion of
numbers stored in registers.

If you use a register as a counter, incrementing it on each
repetition of the macro, that accomplishes the same thing as a
keyboard macro counter. See Number Registers. For most purposes,
it is simpler to use a keyboard macro counter.

17.4 Executing Macros with Variations

In a keyboard macro, you can create an effect similar to that of
query-replace, in that the macro asks you each time around
whether to make a change.

C-x q

When this point is reached during macro execution, ask for confirmation
(kbd-macro-query).

While defining the macro, type C-x q at the point where you
want the query to occur. During macro definition, the C-x q
does nothing, but when you run the macro later, C-x q asks you
interactively whether to continue.

The valid responses when C-x q asks are:

SPC (or y)

Continue executing the keyboard macro.

DEL (or n)

Skip the remainder of this repetition of the macro, and start right
away with the next repetition.

RET (or q)

Skip the remainder of this repetition and cancel further repetitions.

C-r

Enter a recursive editing level, in which you can perform editing
which is not part of the macro. When you exit the recursive edit
using C-M-c, you are asked again how to continue with the
keyboard macro. If you type a SPC at this time, the rest of the
macro definition is executed. It is up to you to leave point and the
text in a state such that the rest of the macro will do what you want.

C-u C-x q, which is C-x q with a numeric argument,
performs a completely different function. It enters a recursive edit
reading input from the keyboard, both when you type it during the
definition of the macro, and when it is executed from the macro. During
definition, the editing you do inside the recursive edit does not become
part of the macro. During macro execution, the recursive edit gives you
a chance to do some particularized editing on each repetition.
See Recursive Edit.

17.5 Naming and Saving Keyboard Macros

Give a command name (for the duration of the Emacs session) to the most
recently defined keyboard macro (kmacro-name-last-macro).

C-x C-k b

Bind the most recently defined keyboard macro to a key sequence (for
the duration of the session) (kmacro-bind-to-key).

M-x insert-kbd-macro

Insert in the buffer a keyboard macro’s definition, as Lisp code.

If you wish to save a keyboard macro for later use, you can give it
a name using C-x C-k n (kmacro-name-last-macro).
This reads a name as an argument using the minibuffer and defines that
name to execute the last keyboard macro, in its current form. (If you
later add to the definition of this macro, that does not alter the
name’s definition as a macro.) The macro name is a Lisp symbol, and
defining it in this way makes it a valid command name for calling with
M-x or for binding a key to with global-set-key
(see Keymaps). If you specify a name that has a prior definition
other than a keyboard macro, an error message is shown and nothing is
changed.

You can also bind the last keyboard macro (in its current form) to a
key, using C-x C-k b (kmacro-bind-to-key) followed by the
key sequence you want to bind. You can bind to any key sequence in
the global keymap, but since most key sequences already have other
bindings, you should select the key sequence carefully. If you try to
bind to a key sequence with an existing binding (in any keymap), this
command asks you for confirmation before replacing the existing binding.

To avoid problems caused by overriding existing bindings, the key
sequences C-x C-k 0 through C-x C-k 9 and C-x C-k A
through C-x C-k Z are reserved for your own keyboard macro
bindings. In fact, to bind to one of these key sequences, you only
need to type the digit or letter rather than the whole key sequences.
For example,

C-x C-k b 4

will bind the last keyboard macro to the key sequence C-x C-k 4.

Once a macro has a command name, you can save its definition in a file.
Then it can be used in another editing session. First, visit the file
you want to save the definition in. Then use this command:

M-x insert-kbd-macro RETmacronameRET

This inserts some Lisp code that, when executed later, will define the
same macro with the same definition it has now. (You need not
understand Lisp code to do this, because insert-kbd-macro writes
the Lisp code for you.) Then save the file. You can load the file
later with load-file (see Lisp Libraries). If the file you
save in is your init file ~/.emacs (see Init File) then the
macro will be defined each time you run Emacs.

If you give insert-kbd-macro a numeric argument, it makes
additional Lisp code to record the keys (if any) that you have bound
to macroname, so that the macro will be reassigned the same keys
when you load the file.

17.6 Editing a Keyboard Macro

Edit the last 300 keystrokes as a keyboard macro
(kmacro-edit-lossage).

You can edit the last keyboard macro by typing C-x C-k C-e or
C-x C-k RET (kmacro-edit-macro). This formats the
macro definition in a buffer and enters a specialized major mode for
editing it. Type C-h m once in that buffer to display details
of how to edit the macro. When you are finished editing, type
C-c C-c.

You can edit a named keyboard macro or a macro bound to a key by typing
C-x C-k e (edit-kbd-macro). Follow that with the
keyboard input that you would use to invoke the macro—C-x e or
M-x name or some other key sequence.

You can edit the last 300 keystrokes as a macro by typing
C-x C-k l (kmacro-edit-lossage).

17.7 Stepwise Editing a Keyboard Macro

You can interactively replay and edit the last keyboard
macro, one command at a time, by typing C-x C-k SPC
(kmacro-step-edit-macro). Unless you quit the macro using
q or C-g, the edited macro replaces the last macro on the
macro ring.

This macro editing feature shows the last macro in the minibuffer
together with the first (or next) command to be executed, and prompts
you for an action. You can enter ? to get a summary of your
options. These actions are available:

SPC and y execute the current command, and advance to the
next command in the keyboard macro.

n, d, and DEL skip and delete the current command.

f skips the current command in this execution of the keyboard
macro, but doesn’t delete it from the macro.

TAB executes the current command, as well as all similar
commands immediately following the current command; for example, TAB
may be used to insert a sequence of characters (corresponding to a
sequence of self-insert-command commands).

c continues execution (without further editing) until the end of
the keyboard macro. If execution terminates normally, the edited
macro replaces the original keyboard macro.

C-k skips and deletes the rest of the keyboard macro,
terminates step-editing, and replaces the original keyboard macro
with the edited macro.

q and C-g cancels the step-editing of the keyboard macro;
discarding any changes made to the keyboard macro.

i key… C-j reads and executes a series of key sequences (not
including the final C-j), and inserts them before the current
command in the keyboard macro, without advancing over the current
command.

I key… reads one key sequence, executes it, and inserts it
before the current command in the keyboard macro, without advancing
over the current command.

r key… C-j reads and executes a series of key sequences (not
including the final C-j), and replaces the current command in
the keyboard macro with them, advancing over the inserted key
sequences.

R key… reads one key sequence, executes it, and replaces the
current command in the keyboard macro with that key sequence,
advancing over the inserted key sequence.

a key… C-j executes the current command, then reads and
executes a series of key sequences (not including the final
C-j), and inserts them after the current command in the keyboard
macro; it then advances over the current command and the inserted key
sequences.

A key… C-j executes the rest of the commands in the keyboard
macro, then reads and executes a series of key sequences (not
including the final C-j), and appends them at the end of the
keyboard macro; it then terminates the step-editing and replaces the
original keyboard macro with the edited macro.

18 File Handling

The operating system stores data permanently in named files, so
most of the text you edit with Emacs comes from a file and is ultimately
stored in a file.

To edit a file, you must tell Emacs to read the file and prepare a
buffer containing a copy of the file’s text. This is called
visiting the file. Editing commands apply directly to text in the
buffer; that is, to the copy inside Emacs. Your changes appear in the
file itself only when you save the buffer back into the file.

In addition to visiting and saving files, Emacs can delete, copy,
rename, and append to files, keep multiple versions of them, and operate
on file directories.

18.1 File Names

Many Emacs commands that operate on a file require you to specify
the file name, using the minibuffer (see Minibuffer File).

While in the minibuffer, you can use the usual completion and
history commands (see Minibuffer). Note that file name completion
ignores file names whose extensions appear in the variable
completion-ignored-extensions (see Completion Options).
Note also that most commands use “permissive completion with
confirmation” for reading file names: you are allowed to submit a
nonexistent file name, but if you type RET immediately after
completing up to a nonexistent file name, Emacs prints
‘[Confirm]’ and you must type a second RET to confirm.
See Completion Exit, for details.

Each buffer has a default directory, stored in the
buffer-local variable default-directory. Whenever Emacs reads
a file name using the minibuffer, it usually inserts the default
directory into the minibuffer as the initial contents. You can
inhibit this insertion by changing the variable
insert-default-directory to nil (see Minibuffer File). Regardless, Emacs always assumes that any relative file name
is relative to the default directory, e.g., entering a file name
without a directory specifies a file in the default directory.

When you visit a file, Emacs sets default-directory in the
visiting buffer to the directory of its file. When you create a new
buffer that is not visiting a file, via a command like C-x b,
its default directory is usually copied from the buffer that was
current at the time (see Select Buffer). You can use the command
M-x pwd to see the value of default-directory in the
current buffer. The command M-x cd prompts for a directory
name, and sets the buffer’s default-directory to that directory
(doing this does not change the buffer’s file name, if any).

As an example, when you visit the file /u/rms/gnu/gnu.tasks,
the default directory is set to /u/rms/gnu/. If you invoke a
command that reads a file name, entering just ‘foo’ in the
minibuffer, with a directory omitted, specifies the file
/u/rms/gnu/foo; entering ‘../.login’ specifies
/u/rms/.login; and entering ‘new/foo’ specifies
/u/rms/gnu/new/foo.

When typing a file name into the minibuffer, you can make use of a
couple of shortcuts: a double slash is interpreted as “ignore
everything before the second slash in the pair”, and ‘~/’ is
interpreted as your home directory. See Minibuffer File.

The character ‘$’ is used to
substitute an environment variable into a file name. The name of the
environment variable consists of all the alphanumeric characters after
the ‘$’; alternatively, it can be enclosed in braces after the
‘$’. For example, if you have used the shell command
export FOO=rms/hacks to set up an environment variable named
FOO, then both /u/$FOO/test.c and
/u/${FOO}/test.c are abbreviations for
/u/rms/hacks/test.c. If the environment variable is not
defined, no substitution occurs, so that the character ‘$’ stands
for itself. Note that environment variables affect Emacs only if they
are applied before Emacs is started.

To access a file with ‘$’ in its name, if the ‘$’ causes
expansion, type ‘$$’. This pair is converted to a single
‘$’ at the same time that variable substitution is performed for
a single ‘$’. Alternatively, quote the whole file name with
‘/:’ (see Quoted File Names). File names which begin with a
literal ‘~’ should also be quoted with ‘/:’.

18.2 Visiting Files

Visit a file for viewing, without allowing changes to it
(find-file-read-only).

C-x C-v

Visit a different file instead of the one visited last
(find-alternate-file).

C-x 4 f

Visit a file, in another window (find-file-other-window). Don’t
alter what is displayed in the selected window.

C-x 5 f

Visit a file, in a new frame (find-file-other-frame). Don’t
alter what is displayed in the selected frame.

M-x find-file-literally

Visit a file with no conversion of the contents.

Visiting a file means reading its contents into an Emacs
buffer so you can edit them. Emacs makes a new buffer for each file
that you visit.

To visit a file, type C-x C-f (find-file) and use the
minibuffer to enter the name of the desired file. While in the
minibuffer, you can abort the command by typing C-g. See File Names, for details about entering file names into minibuffers.

If the specified file exists but the system does not allow you to
read it, an error message is displayed in the echo area. Otherwise,
you can tell that C-x C-f has completed successfully by the
appearance of new text on the screen, and by the buffer name shown in
the mode line (see Mode Line). Emacs normally constructs the
buffer name from the file name, omitting the directory name. For
example, a file named /usr/rms/emacs.tex is visited in a buffer
named ‘emacs.tex’. If there is already a buffer with that name,
Emacs constructs a unique name; the normal method is to add a suffix
based on the directory name (e.g., ‘<rms>’, ‘<tmp>’,
and so on), but you can select other methods. See Uniquify.

To create a new file, just visit it using the same command, C-x
C-f. Emacs displays ‘(New file)’ in the echo area, but in other
respects behaves as if you had visited an existing empty file.

After visiting a file, the changes you make with editing commands are
made in the Emacs buffer. They do not take effect in the visited
file, until you save the buffer (see Saving). If a buffer
contains changes that have not been saved, we say the buffer is
modified. This implies that some changes will be lost if the
buffer is not saved. The mode line displays two stars near the left
margin to indicate that the buffer is modified.

If you visit a file that is already in Emacs, C-x C-f switches
to the existing buffer instead of making another copy. Before doing
so, it checks whether the file has changed since you last visited or
saved it. If the file has changed, Emacs offers to reread it.

If you try to visit a file larger than
large-file-warning-threshold (the default is 10000000, which is
about 10 megabytes), Emacs asks you for confirmation first. You can
answer y to proceed with visiting the file. Note, however, that
Emacs cannot visit files that are larger than the maximum Emacs buffer
size, which is limited by the amount of memory Emacs can allocate and
by the integers that Emacs can represent (see Buffers). If you
try, Emacs displays an error message saying that the maximum buffer
size has been exceeded.

If the file name you specify contains shell-style wildcard
characters, Emacs visits all the files that match it. (On
case-insensitive filesystems, Emacs matches the wildcards disregarding
the letter case.) Wildcards include ‘?’, ‘*’, and
‘[…]’ sequences. To enter the wild card ‘?’ in a file
name in the minibuffer, you need to type C-q ?. See Quoted File Names, for information on how to visit a file whose name
actually contains wildcard characters. You can disable the wildcard
feature by customizing find-file-wildcards.

If you visit the wrong file unintentionally by typing its name
incorrectly, type C-x C-v (find-alternate-file) to visit
the file you really wanted. C-x C-v is similar to C-x
C-f, but it kills the current buffer (after first offering to save it
if it is modified). When C-x C-v reads the file name to visit,
it inserts the entire default file name in the buffer, with point just
after the directory part; this is convenient if you made a slight
error in typing the name.

If you “visit” a file that is actually a directory, Emacs invokes
Dired, the Emacs directory browser. See Dired. You can disable
this behavior by setting the variable find-file-run-dired to
nil; in that case, it is an error to try to visit a directory.

Files which are actually collections of other files, or file
archives, are visited in special modes which invoke a Dired-like
environment to allow operations on archive members. See File Archives, for more about these features.

If you visit a file that the operating system won’t let you modify,
or that is marked read-only, Emacs makes the buffer read-only too, so
that you won’t go ahead and make changes that you’ll have trouble
saving afterward. You can make the buffer writable with C-x C-q
(read-only-mode). See Misc Buffer.

If you want to visit a file as read-only in order to protect
yourself from entering changes accidentally, visit it with the command
C-x C-r (find-file-read-only) instead of C-x C-f.

C-x 4 f (find-file-other-window) is like C-x C-f
except that the buffer containing the specified file is selected in another
window. The window that was selected before C-x 4 f continues to
show the same buffer it was already showing. If this command is used when
only one window is being displayed, that window is split in two, with one
window showing the same buffer as before, and the other one showing the
newly requested file. See Windows.

C-x 5 f (find-file-other-frame) is similar, but opens a
new frame, or selects any existing frame showing the specified file.
See Frames.

On graphical displays, there are two additional methods for visiting
files. Firstly, when Emacs is built with a suitable GUI toolkit,
commands invoked with the mouse (by clicking on the menu bar or tool
bar) use the toolkit’s standard “File Selection” dialog instead of
prompting for the file name in the minibuffer. On GNU/Linux and Unix
platforms, Emacs does this when built with GTK, LessTif, and Motif
toolkits; on MS-Windows and Mac, the GUI version does that by default.
For information on how to customize this, see Dialog Boxes.

Secondly, Emacs supports “drag and drop”: dropping a file into an
ordinary Emacs window visits the file using that window. As an
exception, dropping a file into a window displaying a Dired buffer
moves or copies the file into the displayed directory. For details,
see Drag and Drop, and Misc Dired Features.

On text-mode terminals and on graphical displays when Emacs was
built without a GUI toolkit, you can visit files via the menu-bar
“File” menu, which has a “Visit New File” item.

Each time you visit a file, Emacs automatically scans its contents
to detect what character encoding and end-of-line convention it uses,
and converts these to Emacs’s internal encoding and end-of-line
convention within the buffer. When you save the buffer, Emacs
performs the inverse conversion, writing the file to disk with its
original encoding and end-of-line convention. See Coding Systems.

If you wish to edit a file as a sequence of ASCII
characters with no special encoding or conversion, use the M-x
find-file-literally command. This visits a file, like C-x C-f,
but does not do format conversion (see Format
Conversion in the Emacs Lisp Reference Manual), character code
conversion (see Coding Systems), or automatic uncompression
(see Compressed Files), and does not add a final newline because
of require-final-newline (see Customize Save). If you have
already visited the same file in the usual (non-literal) manner, this
command asks you whether to visit it literally instead.

Two special hook variables allow extensions to modify the operation
of visiting files. Visiting a file that does not exist runs the
functions in find-file-not-found-functions; this variable holds
a list of functions, which are called one by one (with no arguments)
until one of them returns non-nil. This is not a normal hook,
and the name ends in ‘-functions’ rather than ‘-hook’ to
indicate that fact.

Successful visiting of any file, whether existing or not, calls the
functions in find-file-hook, with no arguments. This variable
is a normal hook. In the case of a nonexistent file, the
find-file-not-found-functions are run first. See Hooks.

There are several ways to specify automatically the major mode for
editing the file (see Choosing Modes), and to specify local
variables defined for that file (see File Variables).

18.3.1 Commands for Saving Files

Forget that the current buffer has been changed (not-modified).
With prefix argument (C-u), mark the current buffer as changed.

C-x C-w

Save the current buffer with a specified file name (write-file).

M-x set-visited-file-name

Change the file name under which the current buffer will be saved.

When you wish to save the file and make your changes permanent, type
C-x C-s (save-buffer). After saving is finished, C-x C-s
displays a message like this:

Wrote /u/rms/gnu/gnu.tasks

If the current buffer is not modified (no changes have been made in it
since the buffer was created or last saved), saving is not really
done, because it would have no effect. Instead, C-x C-s
displays a message like this in the echo area:

(No changes need to be saved)

With a prefix argument, C-u C-x C-s, Emacs also marks the buffer
to be backed up when the next save is done. See Backup.

The command C-x s (save-some-buffers) offers to save any
or all modified buffers. It asks you what to do with each buffer. The
possible responses are analogous to those of query-replace:

y

Save this buffer and ask about the rest of the buffers.

n

Don’t save this buffer, but ask about the rest of the buffers.

!

Save this buffer and all the rest with no more questions.

RET

Terminate save-some-buffers without any more saving.

.

Save this buffer, then exit save-some-buffers without even asking
about other buffers.

C-r

View the buffer that you are currently being asked about. When you exit
View mode, you get back to save-some-buffers, which asks the
question again.

d

Diff the buffer against its corresponding file, so you can see what
changes you would be saving. This calls the command
diff-buffer-with-file (see Comparing Files).

C-h

Display a help message about these options.

C-x C-c, the key sequence to exit Emacs, invokes
save-some-buffers and therefore asks the same questions.

If you have changed a buffer but do not wish to save the changes,
you should take some action to prevent it. Otherwise, each time you
use C-x s or C-x C-c, you are liable to save this buffer
by mistake. One thing you can do is type M-~
(not-modified), which clears out the indication that the buffer
is modified. If you do this, none of the save commands will believe
that the buffer needs to be saved. (‘~’ is often used as a
mathematical symbol for ‘not’; thus M-~ is ‘not’, metafied.)
Alternatively, you can cancel all the changes made since the file was
visited or saved, by reading the text from the file again. This is
called reverting. See Reverting. (You could also undo all
the changes by repeating the undo command C-x u until you have
undone all the changes; but reverting is easier.)

M-x set-visited-file-name alters the name of the file that the
current buffer is visiting. It reads the new file name using the
minibuffer. Then it marks the buffer as visiting that file name, and
changes the buffer name correspondingly. set-visited-file-name
does not save the buffer in the newly visited file; it just alters the
records inside Emacs in case you do save later. It also marks the
buffer as “modified” so that C-x C-s in that buffer
will save.

If you wish to mark the buffer as visiting a different file and save
it right away, use C-x C-w (write-file). This is
equivalent to set-visited-file-name followed by C-x C-s,
except that C-x C-w asks for confirmation if the file exists.
C-x C-s used on a buffer that is not visiting a file has the
same effect as C-x C-w; that is, it reads a file name, marks the
buffer as visiting that file, and saves it there. The default file
name in a buffer that is not visiting a file is made by combining the
buffer name with the buffer’s default directory (see File Names).

If the new file name implies a major mode, then C-x C-w switches
to that major mode, in most cases. The command
set-visited-file-name also does this. See Choosing Modes.

If Emacs is about to save a file and sees that the date of the latest
version on disk does not match what Emacs last read or wrote, Emacs
notifies you of this fact, because it probably indicates a problem caused
by simultaneous editing and requires your immediate attention.
See Simultaneous Editing.

18.3.2 Backup Files

On most operating systems, rewriting a file automatically destroys all
record of what the file used to contain. Thus, saving a file from Emacs
throws away the old contents of the file—or it would, except that
Emacs carefully copies the old contents to another file, called the
backup file, before actually saving.

Emacs makes a backup for a file only the first time the file is
saved from a buffer. No matter how many times you subsequently save
the file, its backup remains unchanged. However, if you kill the
buffer and then visit the file again, a new backup file will be made.

For most files, the variable make-backup-files determines
whether to make backup files. On most operating systems, its default
value is t, so that Emacs does write backup files.

For files managed by a version control system (see Version Control), the variable vc-make-backup-files determines whether
to make backup files. By default it is nil, since backup files
are redundant when you store all the previous versions in a version
control system.
See General VC Options.

At your option, Emacs can keep either a single backup for each file,
or make a series of numbered backup files for each file that you edit.
See Backup Names.

The default value of the backup-enable-predicate variable
prevents backup files being written for files in the directories used
for temporary files, specified by temporary-file-directory or
small-temporary-file-directory.

You can explicitly tell Emacs to make another backup file from a
buffer, even though that buffer has been saved before. If you save
the buffer with C-u C-x C-s, the version thus saved will be made
into a backup file if you save the buffer again. C-u C-u C-x
C-s saves the buffer, but first makes the previous file contents into
a new backup file. C-u C-u C-u C-x C-s does both things: it
makes a backup from the previous contents, and arranges to make
another from the newly saved contents if you save again.

18.3.2.1 Single or Numbered Backups

When Emacs makes a backup file, its name is normally constructed by
appending ‘~’ to the file name being edited; thus, the backup
file for eval.c would be eval.c~.

If access control stops Emacs from writing backup files under the
usual names, it writes the backup file as ~/.emacs.d/%backup%~.
Only one such file can exist, so only the most recently made such
backup is available.

Emacs can also make numbered backup files. Numbered backup
file names contain ‘.~’, the number, and another ‘~’ after
the original file name. Thus, the backup files of eval.c would
be called eval.c.~1~, eval.c.~2~, and so on, all the way
through names like eval.c.~259~ and beyond.

The variable version-control determines whether to make
single backup files or multiple numbered backup files. Its possible
values are:

nil

Make numbered backups for files that have numbered backups already.
Otherwise, make single backups. This is the default.

t

Make numbered backups.

never

Never make numbered backups; always make single backups.

The usual way to set this variable is globally, through your init file
or the customization buffer. However, you can set
version-control locally in an individual buffer to control the
making of backups for that buffer’s file (see Locals). You can
have Emacs set version-control locally whenever you visit a
given file (see File Variables). Some modes, such as Rmail mode,
set this variable.

If you set the environment variable VERSION_CONTROL, to tell
various GNU utilities what to do with backup files, Emacs also obeys the
environment variable by setting the Lisp variable version-control
accordingly at startup. If the environment variable’s value is ‘t’
or ‘numbered’, then version-control becomes t; if the
value is ‘nil’ or ‘existing’, then version-control
becomes nil; if it is ‘never’ or ‘simple’, then
version-control becomes never.

You can customize the variable backup-directory-alist to
specify that files matching certain patterns should be backed up in
specific directories. This variable applies to both single and
numbered backups. A typical use is to add an element ("."
. dir) to make all backups in the directory with absolute name
dir; Emacs modifies the backup file names to avoid clashes
between files with the same names originating in different
directories. Alternatively, adding, ("." . ".~") would make
backups in the invisible subdirectory .~ of the original file’s
directory. Emacs creates the directory, if necessary, to make the
backup.

If you set the variable make-backup-file-name-function to
a suitable Lisp function, you can override the usual way Emacs
constructs backup file names.

18.3.2.2 Automatic Deletion of Backups

To prevent excessive consumption of disk space, Emacs can delete numbered
backup versions automatically. Generally Emacs keeps the first few backups
and the latest few backups, deleting any in between. This happens every
time a new backup is made.

The two variables kept-old-versions and
kept-new-versions control this deletion. Their values are,
respectively, the number of oldest (lowest-numbered) backups to keep
and the number of newest (highest-numbered) ones to keep, each time a
new backup is made. The backups in the middle (excluding those oldest
and newest) are the excess middle versions—those backups are
deleted. These variables’ values are used when it is time to delete
excess versions, just after a new backup version is made; the newly
made backup is included in the count in kept-new-versions. By
default, both variables are 2.

If delete-old-versions is t, Emacs deletes the excess
backup files silently. If it is nil, the default, Emacs asks
you whether it should delete the excess backup versions. If it has
any other value, then Emacs never automatically deletes backups.

Dired’s . (Period) command can also be used to delete old versions.
See Dired Deletion.

18.3.2.3 Copying vs. Renaming

Backup files can be made by copying the old file or by renaming it.
This makes a difference when the old file has multiple names (hard
links). If the old file is renamed into the backup file, then the
alternate names become names for the backup file. If the old file is
copied instead, then the alternate names remain names for the file
that you are editing, and the contents accessed by those names will be
the new contents.

The method of making a backup file may also affect the file’s owner
and group. If copying is used, these do not change. If renaming is used,
you become the file’s owner, and the file’s group becomes the default
(different operating systems have different defaults for the group).

The choice of renaming or copying is made as follows:

If the variable backup-by-copying is non-nil (the
default is nil), use copying.

Otherwise, if the variable backup-by-copying-when-linked is
non-nil (the default is nil), and the file has multiple
names, use copying.

Otherwise, if the variable backup-by-copying-when-mismatch is
non-nil (the default is t), and renaming would change
the file’s owner or group, use copying.

If you change backup-by-copying-when-mismatch to nil,
Emacs checks the numeric user-id of the file’s owner. If this is
higher than backup-by-copying-when-privileged-mismatch, then it
behaves as though backup-by-copying-when-mismatch is
non-nil anyway.

Otherwise, renaming is the default choice.

When a file is managed with a version control system (see Version Control), Emacs does not normally make backups in the usual way for
that file. But check-in and check-out are similar in some ways to
making backups. One unfortunate similarity is that these operations
typically break hard links, disconnecting the file name you visited from
any alternate names for the same file. This has nothing to do with
Emacs—the version control system does it.

18.3.3 Customizing Saving of Files

If the value of the variable require-final-newline is
t, saving or writing a file silently puts a newline at the end
if there isn’t already one there. If the value is visit, Emacs
adds a newline at the end of any file that doesn’t have one, just
after it visits the file. (This marks the buffer as modified, and you
can undo it.) If the value is visit-save, Emacs adds such
newlines both on visiting and on saving. If the value is nil,
Emacs leaves the end of the file unchanged; any other non-nil
value means to asks you whether to add a newline. The default is
nil.

Some major modes are designed for specific kinds of files that are
always supposed to end in newlines. Such major modes set the variable
require-final-newline to the value of
mode-require-final-newline, which defaults to t. By
setting the latter variable, you can control how these modes handle
final newlines.

Normally, when a program writes a file, the operating system briefly
caches the file’s data in main memory before committing the data to
disk. This can greatly improve performance; for example, when running
on laptops, it can avoid a disk spin-up each time a file is written.
However, it risks data loss if the operating system crashes before
committing the cache to disk.

To lessen this risk, Emacs can invoke the fsync system call
after saving a file. Using fsync does not eliminate the risk
of data loss, partly because many systems do not implement
fsync properly, and partly because Emacs’s file-saving
procedure typically relies also on directory updates that might not
survive a crash even if fsync works properly.

The write-region-inhibit-fsync variable controls whether
Emacs invokes fsync after saving a file. The variable’s
default value is nil when Emacs is interactive, and t
when Emacs runs in batch mode.

18.3.4 Protection against Simultaneous Editing

Simultaneous editing occurs when two users visit the same file, both
make changes, and then both save them. If nobody is informed that
this is happening, whichever user saves first would later find that
his changes were lost.

On some systems, Emacs notices immediately when the second user starts
to change the file, and issues an immediate warning. On all systems,
Emacs checks when you save the file, and warns if you are about to
overwrite another user’s changes. You can prevent loss of the other
user’s work by taking the proper corrective action instead of saving the
file.

When you make the first modification in an Emacs buffer that is
visiting a file, Emacs records that the file is locked by you.
(It does this by creating a specially-named symbolic link7 with special contents in the same directory.) Emacs removes the lock
when you save the changes. The idea is that the file is locked
whenever an Emacs buffer visiting it has unsaved changes.

You can prevent the creation of lock files by setting the variable
create-lockfiles to nil. Caution: by
doing so you will lose the benefits that this feature provides.

If you begin to modify the buffer while the visited file is locked by
someone else, this constitutes a collision. When Emacs detects a
collision, it asks you what to do, by calling the Lisp function
ask-user-about-lock. You can redefine this function for the sake
of customization. The standard definition of this function asks you a
question and accepts three possible answers:

s

Steal the lock. Whoever was already changing the file loses the lock,
and you gain the lock.

p

Proceed. Go ahead and edit the file despite its being locked by someone else.

q

Quit. This causes an error (file-locked), and the buffer
contents remain unchanged—the modification you were trying to make
does not actually take place.

If Emacs or the operating system crashes, this may leave behind lock
files which are stale, so you may occasionally get warnings about
spurious collisions. When you determine that the collision is
spurious, just use p to tell Emacs to go ahead anyway.

Note that locking works on the basis of a file name; if a file has
multiple names, Emacs does not prevent two users from editing it
simultaneously under different names.

A lock file cannot be written in some circumstances, e.g., if Emacs
lacks the system permissions or cannot create lock files for some
other reason. In these cases, Emacs can still detect the collision
when you try to save a file, by checking the file’s last-modification
date. If the file has changed since the last time Emacs visited or
saved it, that implies that changes have been made in some other way,
and will be lost if Emacs proceeds with saving. Emacs then displays a
warning message and asks for confirmation before saving; answer
yes to save, and no or C-g cancel the save.

If you are notified that simultaneous editing has already taken
place, one way to compare the buffer to its file is the M-x
diff-buffer-with-file command. See Comparing Files.

18.3.5 Shadowing Files

Make all files that match each of a group of files be shared between hosts.

M-x shadow-define-cluster RETnameRET

Define a shadow file cluster name.

M-x shadow-copy-files

Copy all pending shadow files.

M-x shadow-cancel

Cancel the instruction to shadow some files.

You can arrange to keep identical shadow copies of certain files
in more than one place—possibly on different machines. To do this,
first you must set up a shadow file group, which is a set of
identically-named files shared between a list of sites. The file
group is permanent and applies to further Emacs sessions as well as
the current one. Once the group is set up, every time you exit Emacs,
it will copy the file you edited to the other files in its group. You
can also do the copying without exiting Emacs, by typing M-x
shadow-copy-files.

To set up a shadow file group, use M-x
shadow-define-literal-group or M-x shadow-define-regexp-group.
See their documentation strings for further information.

Before copying a file to its shadows, Emacs asks for confirmation.
You can answer “no” to bypass copying of this file, this time. If
you want to cancel the shadowing permanently for a certain file, use
M-x shadow-cancel to eliminate or change the shadow file group.

A shadow cluster is a group of hosts that share directories, so
that copying to or from one of them is sufficient to update the file
on all of them. Each shadow cluster has a name, and specifies the
network address of a primary host (the one we copy files to), and a
regular expression that matches the host names of all the other hosts
in the cluster. You can define a shadow cluster with M-x
shadow-define-cluster.

18.3.6 Updating Time Stamps Automatically

You can arrange to put a time stamp in a file, so that it is updated
automatically each time you edit and save the file. The time stamp
must be in the first eight lines of the file, and you should insert it
like this:

Time-stamp: <>

or like this:

Time-stamp: " "

Then add the function time-stamp to the hook
before-save-hook (see Hooks). When you save the file, this
function then automatically updates the time stamp with the current
date and time. You can also use the command M-x time-stamp to
update the time stamp manually. For other customizations, see the
Custom group time-stamp. Note that the time stamp is formatted
according to your locale setting (see Environment).

18.4 Reverting a Buffer

If you have made extensive changes to a file-visiting buffer and
then change your mind, you can revert the changes and go back to
the saved version of the file. To do this, type M-x
revert-buffer. Since reverting unintentionally could lose a lot of
work, Emacs asks for confirmation first.

The revert-buffer command tries to position point in such a
way that, if the file was edited only slightly, you will be at
approximately the same part of the text as before. But if you have
made major changes, point may end up in a totally different location.

Reverting marks the buffer as “not modified”. It also clears the
buffer’s undo history (see Undo). Thus, the reversion cannot be
undone—if you change your mind yet again, you can’t use the undo
commands to bring the reverted changes back.

Some kinds of buffers that are not associated with files, such as
Dired buffers, can also be reverted. For them, reverting means
recalculating their contents. Buffers created explicitly with
C-x b cannot be reverted; revert-buffer reports an error
if you try.

When you edit a file that changes automatically and frequently—for
example, a log of output from a process that continues to run—it may
be useful for Emacs to revert the file without querying you. To
request this behavior, set the variable revert-without-query to
a list of regular expressions. When a file name matches one of these
regular expressions, find-file and revert-buffer will
revert it automatically if it has changed—provided the buffer itself
is not modified. (If you have edited the text, it would be wrong to
discard your changes.)

You can also tell Emacs to revert buffers periodically. To do this
for a specific buffer, enable the minor mode Auto-Revert mode by
typing M-x auto-revert-mode. This automatically reverts the
current buffer every five seconds; you can change the interval through
the variable auto-revert-interval. To do the same for all file
buffers, type M-x global-auto-revert-mode to enable Global
Auto-Revert mode. These minor modes do not check or revert remote
files, because that is usually too slow.

One use of Auto-Revert mode is to “tail” a file such as a system
log, so that changes made to that file by other programs are
continuously displayed. To do this, just move the point to the end of
the buffer, and it will stay there as the file contents change.
However, if you are sure that the file will only change by growing at
the end, use Auto-Revert Tail mode instead
(auto-revert-tail-mode). It is more efficient for this.
Auto-Revert Tail mode works also for remote files.

See VC Undo, for commands to revert to earlier versions of files
under version control. See VC Mode Line, for Auto Revert
peculiarities when visiting files under version control.

18.5 Auto Reverting Non-File Buffers

Global Auto Revert Mode normally only reverts file buffers. There are
two ways to auto-revert certain non-file buffers: by enabling Auto
Revert Mode in those buffers (using M-x auto-revert-mode); and
by setting global-auto-revert-non-file-buffers to a
non-nil value. The latter enables Auto Reverting for all types
of buffers for which it is implemented (listed in the menu below).

Like file buffers, non-file buffers should normally not revert while
you are working on them, or while they contain information that might
get lost after reverting. Therefore, they do not revert if they are
“modified”. This can get tricky, because deciding when a non-file
buffer should be marked modified is usually more difficult than for
file buffers.

Another tricky detail is that, for efficiency reasons, Auto Revert
often does not try to detect all possible changes in the buffer, only
changes that are “major” or easy to detect. Hence, enabling
auto-reverting for a non-file buffer does not always guarantee that
all information in the buffer is up-to-date, and does not necessarily
make manual reverts useless.

At the other extreme, certain buffers automatically revert every
auto-revert-interval seconds. (This currently only applies to
the Buffer Menu.) In this case, Auto Revert does not print any
messages while reverting, even when auto-revert-verbose is
non-nil.

The details depend on the particular types of buffers and are
explained in the corresponding sections.

18.5.1 Auto Reverting the Buffer Menu

If auto-reverting of non-file buffers is enabled, the Buffer Menu
automatically reverts every auto-revert-interval seconds,
whether there is a need for it or not. (It would probably take longer
to check whether there is a need than to actually revert.)

If the Buffer Menu inappropriately gets marked modified, just revert
it manually using g and auto-reverting will resume. However, if
you marked certain buffers to get deleted or to be displayed, you have
to be careful, because reverting erases all marks. The fact that
adding marks sets the buffer’s modified flag prevents Auto Revert from
automatically erasing the marks.

18.5.2 Auto Reverting Dired buffers

Auto-reverting Dired buffers currently works on GNU or Unix style
operating systems. It may not work satisfactorily on some other
systems.

Dired buffers only auto-revert when the file list of the buffer’s main
directory changes (e.g., when a new file is added). They do not
auto-revert when information about a particular file changes
(e.g., when the size changes) or when inserted subdirectories change.
To be sure that all listed information is up to date, you have
to manually revert using g, even if auto-reverting is
enabled in the Dired buffer. Sometimes, you might get the impression
that modifying or saving files listed in the main directory actually
does cause auto-reverting. This is because making changes to a file,
or saving it, very often causes changes in the directory itself; for
instance, through backup files or auto-save files. However, this is
not guaranteed.

If the Dired buffer is marked modified and there are no changes you
want to protect, then most of the time you can make auto-reverting
resume by manually reverting the buffer using g. There is one
exception. If you flag or mark files, you can safely revert the
buffer. This will not erase the flags or marks (unless the marked
file has been deleted, of course). However, the buffer will stay
modified, even after reverting, and auto-reverting will not resume.
This is because, if you flag or mark files, you may be working on the
buffer and you might not want the buffer to change without warning.
If you want auto-reverting to resume in the presence of marks and
flags, mark the buffer non-modified using M-~. However, adding,
deleting or changing marks or flags will mark it modified again.

Remote Dired buffers are not auto-reverted (because it may be slow).
Neither are Dired buffers for which you used shell wildcards or file
arguments to list only some of the files. *Find* and
*Locate* buffers do not auto-revert either.

18.5.3 Adding Support for Auto-Reverting additional Buffers.

This section is intended for Elisp programmers who would like to add
support for auto-reverting new types of buffers.

To support auto-reverting the buffer must first of all have a suitable
revert-buffer-function. See Reverting in the Emacs Lisp Reference Manual.

In addition, it must have a suitable buffer-stale-function.

Variable: buffer-stale-function

The value of this variable is a function to check whether a
buffer needs reverting. This should be a function with one optional
argument noconfirm. The function should return non-nil
if the buffer should be reverted. The buffer is current when this
function is called.

While this function is mainly intended for use in auto-reverting, it
could be used for other purposes as well. For instance, if
auto-reverting is not enabled, it could be used to warn the user that
the buffer needs reverting. The idea behind the noconfirm
argument is that it should be t if the buffer is going to be
reverted without asking the user and nil if the function is
just going to be used to warn the user that the buffer is out of date.
In particular, for use in auto-reverting, noconfirm is t.
If the function is only going to be used for auto-reverting, you can
ignore the noconfirm argument.

If you just want to automatically auto-revert every
auto-revert-interval seconds (like the Buffer Menu), use:

The special return value ‘fast’ tells the caller that the need
for reverting was not checked, but that reverting the buffer is fast.
It also tells Auto Revert not to print any revert messages, even if
auto-revert-verbose is non-nil. This is important, as
getting revert messages every auto-revert-interval seconds can
be very annoying. The information provided by this return value could
also be useful if the function is consulted for purposes other than
auto-reverting.

Once the buffer has a suitable revert-buffer-function and
buffer-stale-function, several problems usually remain.

The buffer will only auto-revert if it is marked unmodified. Hence,
you will have to make sure that various functions mark the buffer
modified if and only if either the buffer contains information that
might be lost by reverting, or there is reason to believe that the user
might be inconvenienced by auto-reverting, because he is actively
working on the buffer. The user can always override this by manually
adjusting the modified status of the buffer. To support this, calling
the revert-buffer-function on a buffer that is marked
unmodified should always keep the buffer marked unmodified.

It is important to assure that point does not continuously jump around
as a consequence of auto-reverting. Of course, moving point might be
inevitable if the buffer radically changes.

You should make sure that the revert-buffer-function does not
print messages that unnecessarily duplicate Auto Revert’s own messages,
displayed if auto-revert-verbose is t, and effectively
override a nil value for auto-revert-verbose. Hence,
adapting a mode for auto-reverting often involves getting rid of such
messages. This is especially important for buffers that automatically
revert every auto-revert-interval seconds.

If the new auto-reverting is part of Emacs, you should mention it
in the documentation string of global-auto-revert-non-file-buffers.

Similarly, you should add a section to this chapter. This section
should at the very least make clear whether enabling auto-reverting
for the buffer reliably assures that all information in the buffer is
completely up to date (or will be after auto-revert-interval
seconds).

18.6 Auto-Saving: Protection Against Disasters

From time to time, Emacs automatically saves each visited file in a
separate file, without altering the file you actually use. This is
called auto-saving. It prevents you from losing more than a
limited amount of work if the system crashes.

When Emacs determines that it is time for auto-saving, it considers
each buffer, and each is auto-saved if auto-saving is enabled for it
and it has been changed since the last time it was auto-saved. The
message ‘Auto-saving...’ is displayed in the echo area during
auto-saving, if any files are actually auto-saved. Errors occurring
during auto-saving are caught so that they do not interfere with the
execution of commands you have been typing.

18.6.1 Auto-Save Files

Auto-saving does not normally save in the files that you visited,
because it can be very undesirable to save a change that you did not
want to make permanent. Instead, auto-saving is done in a different
file called the auto-save file, and the visited file is changed
only when you request saving explicitly (such as with C-x C-s).

Normally, the auto-save file name is made by appending ‘#’ to the
front and rear of the visited file name. Thus, a buffer visiting file
foo.c is auto-saved in a file #foo.c#. Most buffers that
are not visiting files are auto-saved only if you request it explicitly;
when they are auto-saved, the auto-save file name is made by appending
‘#’ to the front and rear of buffer name, then
adding digits and letters at the end for uniqueness. For
example, the *mail* buffer in which you compose messages to be
sent might be auto-saved in a file named #*mail*#704juu. Auto-save file
names are made this way unless you reprogram parts of Emacs to do
something different (the functions make-auto-save-file-name and
auto-save-file-name-p). The file name to be used for auto-saving
in a buffer is calculated when auto-saving is turned on in that buffer.

The variable auto-save-file-name-transforms allows a degree
of control over the auto-save file name. It lets you specify a series
of regular expressions and replacements to transform the auto save
file name. The default value puts the auto-save files for remote
files (see Remote Files) into the temporary file directory on the
local machine.

When you delete a substantial part of the text in a large buffer, auto
save turns off temporarily in that buffer. This is because if you
deleted the text unintentionally, you might find the auto-save file more
useful if it contains the deleted text. To reenable auto-saving after
this happens, save the buffer with C-x C-s, or use C-u 1 M-x
auto-save-mode.

If you want auto-saving to be done in the visited file rather than
in a separate auto-save file, set the variable
auto-save-visited-file-name to a non-nil value. In this
mode, there is no real difference between auto-saving and explicit
saving.

A buffer’s auto-save file is deleted when you save the buffer in its
visited file. (You can inhibit this by setting the variable
delete-auto-save-files to nil.) Changing the visited
file name with C-x C-w or set-visited-file-name renames
any auto-save file to go with the new visited name.

18.6.2 Controlling Auto-Saving

Each time you visit a file, auto-saving is turned on for that file’s
buffer if the variable auto-save-default is non-nil (but
not in batch mode; see Initial Options). The default for this
variable is t, so auto-saving is the usual practice for
file-visiting buffers. To toggle auto-saving in the current buffer,
type M-x auto-save-mode. Auto Save mode acts as a buffer-local
minor mode (see Minor Modes).

Emacs auto-saves periodically based on how many characters you have
typed since the last auto-save. The variable
auto-save-interval specifies how many characters there are
between auto-saves. By default, it is 300. Emacs doesn’t accept
values that are too small: if you customize auto-save-interval
to a value less than 20, Emacs will behave as if the value is 20.

Auto-saving also takes place when you stop typing for a while. By
default, it does this after 30 seconds of idleness (at this time,
Emacs may also perform garbage collection; see Garbage
Collection in The Emacs Lisp Reference Manual). To change
this interval, customize the variable auto-save-timeout. The
actual time period is longer if the current buffer is long; this is a
heuristic which aims to keep out of your way when you are editing long
buffers, in which auto-save takes an appreciable amount of time.
Auto-saving during idle periods accomplishes two things: first, it
makes sure all your work is saved if you go away from the terminal for
a while; second, it may avoid some auto-saving while you are actually
typing.

Emacs also does auto-saving whenever it gets a fatal error. This
includes killing the Emacs job with a shell command such as ‘kill
%emacs’, or disconnecting a phone line or network connection.

You can perform an auto-save explicitly with the command M-x
do-auto-save.

18.6.3 Recovering Data from Auto-Saves

You can use the contents of an auto-save file to recover from a loss
of data with the command M-x recover-file RETfileRET. This visits file and then (after your confirmation)
restores the contents from its auto-save file #file#.
You can then save with C-x C-s to put the recovered text into
file itself. For example, to recover file foo.c from its
auto-save file #foo.c#, do:

M-x recover-file RET foo.c RET
yes RET
C-x C-s

Before asking for confirmation, M-x recover-file displays a
directory listing describing the specified file and the auto-save file,
so you can compare their sizes and dates. If the auto-save file
is older, M-x recover-file does not offer to read it.

If Emacs or the computer crashes, you can recover all the files you
were editing from their auto save files with the command M-x
recover-session. This first shows you a list of recorded interrupted
sessions. Move point to the one you choose, and type C-c C-c.

Then recover-session asks about each of the files that were
being edited during that session, asking whether to recover that file.
If you answer y, it calls recover-file, which works in its
normal fashion. It shows the dates of the original file and its
auto-save file, and asks once again whether to recover that file.

When recover-session is done, the files you’ve chosen to
recover are present in Emacs buffers. You should then save them. Only
this—saving them—updates the files themselves.

Emacs records information about interrupted sessions in files named
.saves-pid-hostname in the directory
~/.emacs.d/auto-save-list/. This directory is determined by
the variable auto-save-list-file-prefix. If you set
auto-save-list-file-prefix to nil, sessions are not
recorded for recovery.

18.7 File Name Aliases

Symbolic links and hard links both make it possible for several file
names to refer to the same file. Hard links are alternate names that
refer directly to the file; all the names are equally valid, and no one
of them is preferred. By contrast, a symbolic link is a kind of defined
alias: when foo is a symbolic link to bar, you can use
either name to refer to the file, but bar is the real name, while
foo is just an alias. More complex cases occur when symbolic
links point to directories.

Normally, if you visit a file which Emacs is already visiting under
a different name, Emacs displays a message in the echo area and uses
the existing buffer visiting that file. This can happen on systems
that support hard or symbolic links, or if you use a long file name on
a system that truncates long file names, or on a case-insensitive file
system. You can suppress the message by setting the variable
find-file-suppress-same-file-warnings to a non-nil
value. You can disable this feature entirely by setting the variable
find-file-existing-other-name to nil: then if you visit
the same file under two different names, you get a separate buffer for
each file name.

If the variable find-file-visit-truename is non-nil,
then the file name recorded for a buffer is the file’s truename
(made by replacing all symbolic links with their target names), rather
than the name you specify. Setting find-file-visit-truename also
implies the effect of find-file-existing-other-name.

Sometimes, a directory is ordinarily accessed through a symbolic
link, and you may want Emacs to preferentially show its “linked”
name. To do this, customize directory-abbrev-alist. Each
element in this list should have the form (from
. to), which means to replace from with to whenever
from appears in a directory name. The from string is a
regular expression (see Regexps). It is matched against directory
names anchored at the first character, and should start with ‘\`’
(to support directory names with embedded newlines, which would defeat
‘^’). The to string should be an ordinary absolute
directory name pointing to the same directory. Do not use ‘~’ to
stand for a home directory in the to string; Emacs performs
these substitutions separately. Here’s an example, from a system on
which /home/fsf is normally accessed through a symbolic link
named /fsf:

18.8 File Directories

The file system groups files into directories. A directory
listing is a list of all the files in a directory. Emacs provides
commands to create and delete directories, and to make directory
listings in brief format (file names only) and verbose format (sizes,
dates, and authors included). Emacs also includes a directory browser
feature called Dired; see Dired.

C-x C-d dir-or-patternRET

Display a brief directory listing (list-directory).

C-u C-x C-d dir-or-patternRET

Display a verbose directory listing.

M-x make-directory RETdirnameRET

Create a new directory named dirname.

M-x delete-directory RETdirnameRET

Delete the directory named dirname. If it isn’t empty,
you will be asked whether you want to delete it recursively.

The command to display a directory listing is C-x C-d
(list-directory). It reads using the minibuffer a file name
which is either a directory to be listed or a wildcard-containing
pattern for the files to be listed. For example,

C-x C-d /u2/emacs/etc RET

lists all the files in directory /u2/emacs/etc. Here is an
example of specifying a file name pattern:

C-x C-d /u2/emacs/src/*.c RET

Normally, C-x C-d displays a brief directory listing containing
just file names. A numeric argument (regardless of value) tells it to
make a verbose listing including sizes, dates, and owners (like
‘ls -l’).

The text of a directory listing is mostly obtained by running
ls in an inferior process. Two Emacs variables control the
switches passed to ls: list-directory-brief-switches is
a string giving the switches to use in brief listings ("-CF" by
default), and list-directory-verbose-switches is a string
giving the switches to use in a verbose listing ("-l" by
default).

In verbose directory listings, Emacs adds information about the
amount of free space on the disk that contains the directory. To do
this, it runs the program specified by
directory-free-space-program with arguments
directory-free-space-args.

The command M-x delete-directory prompts for a directory name
using the minibuffer, and deletes the directory if it is empty. If
the directory is not empty, you will be asked whether you want to
delete it recursively. On systems that have a “Trash” (or “Recycle
Bin”) feature, you can make this command move the specified directory
to the Trash instead of deleting it outright, by changing the variable
delete-by-moving-to-trash to t. See Misc File Ops,
for more information about using the Trash.

18.9 Comparing Files

The command M-x diff prompts for two file names, using the
minibuffer, and displays the differences between the two files in a
buffer named *diff*. This works by running the diff
program, using options taken from the variable diff-switches.
The value of diff-switches should be a string; the default is
"-c" to specify a context diff.
See Diff in Comparing and Merging Files, for more
information about the diff program.

The output of the diff command is shown using a major mode
called Diff mode. See Diff Mode.

The command M-x diff-backup compares a specified file with its
most recent backup. If you specify the name of a backup file,
diff-backup compares it with the source file that it is a
backup of. In all other respects, this behaves like M-x diff.

The command M-x diff-buffer-with-file compares a specified
buffer with its corresponding file. This shows you what changes you
would make to the file if you save the buffer.

The command M-x compare-windows compares the text in the
current window with that in the next window. (For more information
about windows in Emacs, Windows.) Comparison starts at point in
each window, after pushing each initial point value on the mark ring
in its respective buffer. Then it moves point forward in each window,
one character at a time, until it reaches characters that don’t match.
Then the command exits.

If point in the two windows is followed by non-matching text when
the command starts, M-x compare-windows tries heuristically to
advance up to matching text in the two windows, and then exits. So if
you use M-x compare-windows repeatedly, each time it either
skips one matching range or finds the start of another.

With a numeric argument, compare-windows ignores changes in
whitespace. If the variable compare-ignore-case is
non-nil, the comparison ignores differences in case as well.
If the variable compare-ignore-whitespace is non-nil,
compare-windows normally ignores changes in whitespace, and a
prefix argument turns that off.

You can use M-x smerge-mode to turn on Smerge mode, a minor
mode for editing output from the diff3 program. This is
typically the result of a failed merge from a version control system
“update” outside VC, due to conflicting changes to a file. Smerge
mode provides commands to resolve conflicts by selecting specific
changes.

See Emerge,
for the Emerge facility, which provides a powerful interface for
merging files.

18.10 Diff Mode

Diff mode is a major mode used for the output of M-x diff and
other similar commands. This kind of output is called a patch,
because it can be passed to the patch command to
automatically apply the specified changes. To select Diff mode
manually, type M-x diff-mode.

The changes specified in a patch are grouped into hunks, which
are contiguous chunks of text that contain one or more changed lines.
Hunks can also include unchanged lines to provide context for the
changes. Each hunk is preceded by a hunk header, which
specifies the old and new line numbers at which the hunk occurs. Diff
mode highlights each hunk header, to distinguish it from the actual
contents of the hunk.

You can edit a Diff mode buffer like any other buffer. (If it is
read-only, you need to make it writable first. See Misc Buffer.)
Whenever you change a hunk, Diff mode attempts to automatically
correct the line numbers in the hunk headers, to ensure that the patch
remains “correct”. To disable automatic line number correction,
change the variable diff-update-on-the-fly to nil.

Diff mode treats each hunk as an “error message”, similar to
Compilation mode. Thus, you can use commands such as C-x ' to
visit the corresponding source locations. See Compilation Mode.

In addition, Diff mode provides the following commands to navigate,
manipulate and apply parts of patches:

M-n

Move to the next hunk-start (diff-hunk-next).

This command has a side effect: it refines the hunk you move to,
highlighting its changes with better granularity. To disable this
feature, type M-x diff-auto-refine-mode to toggle off the minor
mode Diff Auto-Refine mode. To disable Diff Auto Refine mode by
default, add this to your init file (see Hooks):

(add-hook 'diff-mode-hook
(lambda () (diff-auto-refine-mode -1)))

M-p

Move to the previous hunk-start (diff-hunk-prev). Like
M-n, this has the side-effect of refining the hunk you move to,
unless you disable Diff Auto-Refine mode.

M-}

Move to the next file-start, in a multi-file patch
(diff-file-next).

M-{

Move to the previous file-start, in a multi-file patch
(diff-file-prev).

M-k

Kill the hunk at point (diff-hunk-kill).

M-K

In a multi-file patch, kill the current file part.
(diff-file-kill).

C-c C-a

Apply this hunk to its target file (diff-apply-hunk). With a
prefix argument of C-u, revert this hunk.

C-c C-b

Highlight the changes of the hunk at point with a finer granularity
(diff-refine-hunk). This allows you to see exactly which parts
of each changed line were actually changed.

C-c C-c

Go to the source file and line corresponding to this hunk
(diff-goto-source).

C-c C-e

Start an Ediff session with the patch (diff-ediff-patch).
See Ediff in The Ediff Manual.

C-c C-n

Restrict the view to the current hunk (diff-restrict-view).
See Narrowing. With a prefix argument of C-u, restrict the
view to the current file of a multiple-file patch. To widen again,
use C-x n w (widen).

C-c C-r

Reverse the direction of comparison for the entire buffer
(diff-reverse-direction).

C-c C-s

Split the hunk at point (diff-split-hunk). This is for
manually editing patches, and only works with the unified diff
format produced by the -u or --unified options to
the diff program. If you need to split a hunk in the
context diff format produced by the -c or
--context options to diff, first convert the buffer
to the unified diff format with C-c C-u.

C-c C-d

Convert the entire buffer to the context diff format
(diff-unified->context). With a prefix argument, convert only
the text within the region.

C-c C-u

Convert the entire buffer to unified diff format
(diff-context->unified). With a prefix argument, convert
unified format to context format. When the mark is active, convert
only the text within the region.

C-c C-w

Refine the current hunk so that it disregards changes in whitespace
(diff-refine-hunk).

C-x 4 A

Generate a ChangeLog entry, like C-x 4 a does (see Change Log), for each one of the hunks
(diff-add-change-log-entries-other-window). This creates a
skeleton of the log of changes that you can later fill with the actual
descriptions of the changes. C-x 4 a itself in Diff mode
operates on behalf of the current hunk’s file, but gets the function
name from the patch itself. This is useful for making log entries for
functions that are deleted by the patch.

Patches sometimes include trailing whitespace on modified lines, as
an unintentional and undesired change. There are two ways to deal
with this problem. Firstly, if you enable Whitespace mode in a Diff
buffer (see Useless Whitespace), it automatically highlights
trailing whitespace in modified lines. Secondly, you can use the
command M-x diff-delete-trailing-whitespace, which searches for
trailing whitespace in the lines modified by the patch, and removes
that whitespace in both the patch and the patched source file(s).
This command does not save the modifications that it makes, so you can
decide whether to save the changes (the list of modified files is
displayed in the echo area). With a prefix argument, it tries to
modify the original source files rather than the patched source files.

18.11 Miscellaneous File Operations

Emacs has commands for performing many other operations on files.
All operate on one file; they do not accept wildcard file names.

M-x delete-file prompts for a file and deletes it. If you are
deleting many files in one directory, it may be more convenient to use
Dired rather than delete-file. See Dired Deletion.

M-x move-file-to-trash moves a file into the system
Trash (or Recycle Bin). This is a facility available on
most operating systems; files that are moved into the Trash can be
brought back later if you change your mind.

By default, Emacs deletion commands do not use the Trash. To
use the Trash (when it is available) for common deletion commands,
change the variable delete-by-moving-to-trash to t.
This affects the commands M-x delete-file and M-x
delete-directory (see Directories), as well as the deletion
commands in Dired (see Dired Deletion). Supplying a prefix
argument to M-x delete-file or M-x delete-directory makes
them delete outright, instead of using the Trash, regardless of
delete-by-moving-to-trash.

M-x copy-file reads the file old and writes a new file
named new with the same contents.

M-x copy-directory copies directories, similar to the
cp -r shell command. It prompts for a directory old
and a destination new. If new is an existing directory,
it creates a copy of the old directory and puts it in new.
If new is not an existing directory, it copies all the contents
of old into a new directory named new.

M-x rename-file reads two file names old and new
using the minibuffer, then renames file old as new. If
the file name new already exists, you must confirm with
yes or renaming is not done; this is because renaming causes the
old meaning of the name new to be lost. If old and
new are on different file systems, the file old is copied
and deleted. If the argument new is just a directory name, the
real new name is in that directory, with the same non-directory
component as old. For example, M-x rename-file RET
~/foo RET /tmp RET renames ~/foo to
/tmp/foo. The same rule applies to all the remaining commands
in this section. All of them ask for confirmation when the new file
name already exists, too.

M-x add-name-to-file adds an additional name to an existing
file without removing its old name. The new name is created as a
“hard link” to the existing file. The new name must belong on the
same file system that the file is on. On MS-Windows, this command
works only if the file resides in an NTFS file system. On MS-DOS, it
works by copying the file.

M-x make-symbolic-link reads two file names target and
linkname, then creates a symbolic link named linkname,
which points at target. The effect is that future attempts to
open file linkname will refer to whatever file is named
target at the time the opening is done, or will get an error if
the name target is nonexistent at that time. This command does
not expand the argument target, so that it allows you to specify
a relative name as the target of the link. On MS-Windows, this
command works only on MS Windows Vista and later.

M-x insert-file (also C-x i) inserts a copy of the
contents of the specified file into the current buffer at point,
leaving point unchanged before the contents. The position after the
inserted contents is added to the mark ring, without activating the
mark (see Mark Ring).

M-x insert-file-literally is like M-x insert-file,
except the file is inserted “literally”: it is treated as a sequence
of ASCII characters with no special encoding or conversion,
similar to the M-x find-file-literally command
(see Visiting).

M-x write-region is the inverse of M-x insert-file; it
copies the contents of the region into the specified file. M-x
append-to-file adds the text of the region to the end of the
specified file. See Accumulating Text. The variable
write-region-inhibit-fsync applies to these commands, as well
as saving files; see Customize Save.

M-x set-file-modes reads a file name followed by a file
mode, and applies that file mode to the specified file. File modes,
also called file permissions, determine whether a file can be
read, written to, or executed, and by whom. This command reads file
modes using the same symbolic or octal format accepted by the
chmod command; for instance, ‘u+x’ means to add
execution permission for the user who owns the file. It has no effect
on operating systems that do not support file modes. chmod is a
convenience alias for this function.

18.12 Accessing Compressed Files

Emacs automatically uncompresses compressed files when you visit
them, and automatically recompresses them if you alter them and save
them. Emacs recognizes compressed files by their file names. File
names ending in ‘.gz’ indicate a file compressed with
gzip. Other endings indicate other compression programs.

Automatic uncompression and compression apply to all the operations in
which Emacs uses the contents of a file. This includes visiting it,
saving it, inserting its contents into a buffer, loading it, and byte
compiling it.

To disable this feature, type the command M-x
auto-compression-mode. You can disable it permanently by
customizing the variable auto-compression-mode.

18.13 File Archives

A file whose name ends in ‘.tar’ is normally an archive
made by the tar program. Emacs views these files in a special
mode called Tar mode which provides a Dired-like list of the contents
(see Dired). You can move around through the list just as you
would in Dired, and visit the subfiles contained in the archive.
However, not all Dired commands are available in Tar mode.

If Auto Compression mode is enabled (see Compressed Files), then
Tar mode is used also for compressed archives—files with extensions
‘.tgz’, .tar.Z and .tar.gz.

The keys e, f and RET all extract a component file
into its own buffer. You can edit it there, and if you save the
buffer, the edited version will replace the version in the Tar buffer.
Clicking with the mouse on the file name in the Tar buffer does
likewise. v extracts a file into a buffer in View mode
(see View Mode). o extracts the file and displays it in
another window, so you could edit the file and operate on the archive
simultaneously.

d marks a file for deletion when you later use x, and
u unmarks a file, as in Dired. C copies a file from the
archive to disk and R renames a file within the archive.
g reverts the buffer from the archive on disk. The keys
M, G, and O change the file’s permission bits,
group, and owner, respectively.

Saving the Tar buffer writes a new version of the archive to disk with
the changes you made to the components.

You don’t need the tar program to use Tar mode—Emacs reads
the archives directly. However, accessing compressed archives
requires the appropriate uncompression program.

A separate but similar Archive mode is used for arc,
jar, lzh, zip, rar, 7z, and
zoo archives, as well as exe files that are
self-extracting executables.

The key bindings of Archive mode are similar to those in Tar mode,
with the addition of the m key which marks a file for subsequent
operations, and M-DEL which unmarks all the marked files.
Also, the a key toggles the display of detailed file
information, for those archive types where it won’t fit in a single
line. Operations such as renaming a subfile, or changing its mode or
owner, are supported only for some of the archive formats.

Unlike Tar mode, Archive mode runs the archiving programs to unpack
and repack archives. However, you don’t need these programs to look
at the archive table of contents, only to extract or manipulate the
subfiles in the archive. Details of the program names and their
options can be set in the ‘Archive’ Customize group.

18.14 Remote Files

To carry out this request, Emacs uses a remote-login program such as
ftp, ssh, rlogin, or telnet.
You can always specify in the file name which method to use—for
example, /ftp:user@host:filename uses FTP,
whereas /ssh:user@host:filename uses
ssh. When you don’t specify a method in the file name,
Emacs chooses the method as follows:

If the host name starts with ‘ftp.’ (with dot), Emacs uses FTP.

If the user name is ‘ftp’ or ‘anonymous’, Emacs uses FTP.

If the variable tramp-default-method is set to ‘ftp’,
Emacs uses FTP.

If ssh-agent is running, Emacs uses scp.

Otherwise, Emacs uses ssh.

You can entirely turn off the remote file name feature by setting the
variable tramp-mode to nil. You can turn off the
feature in individual cases by quoting the file name with ‘/:’
(see Quoted File Names).

Remote file access through FTP is handled by the Ange-FTP package, which
is documented in the following. Remote file access through the other
methods is handled by the Tramp package, which has its own manual.
See The Tramp Manual in The Tramp Manual.

When the Ange-FTP package is used, Emacs logs in through FTP using
the name user, if that is specified in the remote file name. If
user is unspecified, Emacs logs in using your user name on the
local system; but if you set the variable ange-ftp-default-user
to a string, that string is used instead. When logging in, Emacs may
also ask for a password.

For performance reasons, Emacs does not make backup files for files
accessed via FTP by default. To make it do so, change the variable
ange-ftp-make-backup-files to a non-nil value.

By default, auto-save files for remote files are made in the
temporary file directory on the local machine, as specified by the
variable auto-save-file-name-transforms. See Auto Save Files.

To visit files accessible by anonymous FTP, you use special user
names ‘anonymous’ or ‘ftp’. Passwords for these user names
are handled specially. The variable
ange-ftp-generate-anonymous-password controls what happens: if
the value of this variable is a string, then that string is used as
the password; if non-nil (the default), then the value of
user-mail-address is used; if nil, then Emacs prompts
you for a password as usual (see Passwords).

Sometimes you may be unable to access files on a remote machine
because a firewall in between blocks the connection for security
reasons. If you can log in on a gateway machine from which the
target files are accessible, and whose FTP server supports
gatewaying features, you can still use remote file names; all you have
to do is specify the name of the gateway machine by setting the
variable ange-ftp-gateway-host, and set
ange-ftp-smart-gateway to t. Otherwise you may be able
to make remote file names work, but the procedure is complex. You can
read the instructions by typing M-x finder-commentary RET
ange-ftp RET.

18.15 Quoted File Names

You can quote an absolute file name to prevent special
characters and syntax in it from having their special effects.
The way to do this is to add ‘/:’ at the beginning.

For example, you can quote a local file name which appears remote, to
prevent it from being treated as a remote file name. Thus, if you have
a directory named /foo: and a file named bar in it, you
can refer to that file in Emacs as ‘/:/foo:/bar’.

‘/:’ can also prevent ‘~’ from being treated as a special
character for a user’s home directory. For example, /:/tmp/~hack
refers to a file whose name is ~hack in directory /tmp.

Quoting with ‘/:’ is also a way to enter in the minibuffer a
file name that contains ‘$’. In order for this to work, the
‘/:’ must be at the beginning of the minibuffer contents. (You
can also double each ‘$’; see File Names with $.)

You can also quote wildcard characters with ‘/:’, for visiting.
For example, /:/tmp/foo*bar visits the file
/tmp/foo*bar.

Another method of getting the same result is to enter
/tmp/foo[*]bar, which is a wildcard specification that matches
only /tmp/foo*bar. However, in many cases there is no need to
quote the wildcard characters because even unquoted they give the
right result. For example, if the only file name in /tmp that
starts with ‘foo’ and ends with ‘bar’ is foo*bar,
then specifying /tmp/foo*bar will visit only
/tmp/foo*bar.

18.16 File Name Cache

You can use the file name cache to make it easy to locate a
file by name, without having to remember exactly where it is located.
When typing a file name in the minibuffer, C-TAB
(file-cache-minibuffer-complete) completes it using the file
name cache. If you repeat C-TAB, that cycles through the
possible completions of what you had originally typed. (However, note
that the C-TAB character cannot be typed on most text
terminals.)

The file name cache does not fill up automatically. Instead, you
load file names into the cache using these commands:

M-x file-cache-add-directory RETdirectoryRET

Add each file name in directory to the file name cache.

M-x file-cache-add-directory-using-find RETdirectoryRET

Add each file name in directory and all of its nested
subdirectories to the file name cache.

M-x file-cache-add-directory-using-locate RETdirectoryRET

Add each file name in directory and all of its nested
subdirectories to the file name cache, using locate to find
them all.

M-x file-cache-add-directory-list RETvariableRET

Add each file name in each directory listed in variable to the
file name cache. variable should be a Lisp variable whose value
is a list of directory names, like load-path.

M-x file-cache-clear-cache RET

Clear the cache; that is, remove all file names from it.

The file name cache is not persistent: it is kept and maintained
only for the duration of the Emacs session. You can view the contents
of the cache with the file-cache-display command.

18.17 Convenience Features for Finding Files

In this section, we introduce some convenient facilities for finding
recently-opened files, reading file names from a buffer, and viewing
image files.

If you enable Recentf mode, with M-x recentf-mode, the
‘File’ menu includes a submenu containing a list of recently
opened files. M-x recentf-save-list saves the current
recent-file-list to a file, and M-x recentf-edit-list
edits it.

The M-x ffap command generalizes find-file with more
powerful heuristic defaults (see FFAP), often based on the text at
point. Partial Completion mode offers other features extending
find-file, which can be used with ffap.
See Completion Options.

Visiting image files automatically selects Image mode. In this
major mode, you can type C-c C-c (image-toggle-display)
to toggle between displaying the file as an image in the Emacs buffer,
and displaying its underlying text (or raw byte) representation.
Displaying the file as an image works only if Emacs is compiled with
support for displaying such images. If the displayed image is wider
or taller than the frame, the usual point motion keys (C-f,
C-p, and so forth) cause different parts of the image to be
displayed. You can press n (image-next-file) and p
(image-previous-file) to visit the next image file and the
previous image file in the same directory, respectively.

If the image can be animated, the command RET
(image-toggle-animation) starts or stops the animation.
Animation plays once, unless the option image-animate-loop is
non-nil. With f (image-next-frame) and b
(image-previous-frame) you can step through the individual
frames. Both commands accept a numeric prefix to step through several
frames at once. You can go to a specific frame with F
(image-goto-frame). Typing a +
(image-increase-speed) increases the speed of the animation,
a - (image-decrease-speed) decreases it, and a r
(image-reverse-speed) reverses it. The command a 0
(image-reset-speed) resets the speed to the original value.

If Emacs was compiled with support for the ImageMagick library, it
can use ImageMagick to render a wide variety of images. The variable
imagemagick-enabled-types lists the image types that Emacs may
render using ImageMagick; each element in the list should be an
internal ImageMagick name for an image type, as a symbol or an
equivalent string (e.g., BMP for .bmp images). To
enable ImageMagick for all possible image types, change
imagemagick-enabled-types to t. The variable
imagemagick-types-inhibit lists the image types which should
never be rendered using ImageMagick, regardless of the value of
imagemagick-enabled-types (the default list includes types like
C and HTML, which ImageMagick can render as an “image”
but Emacs should not). To disable ImageMagick entirely, change
imagemagick-types-inhibit to t.

The Image-Dired package can also be used to view images as
thumbnails. See Image-Dired.

18.18 Filesets

If you regularly edit a certain group of files, you can define them
as a fileset. This lets you perform certain operations, such as
visiting, query-replace, and shell commands on all the files at
once. To make use of filesets, you must first add the expression
(filesets-init) to your init file (see Init File). This
adds a ‘Filesets’ menu to the menu bar.

The simplest way to define a fileset is by adding files to it one at
a time. To add a file to fileset name, visit the file and type
M-x filesets-add-buffer RETnameRET. If
there is no fileset name, this creates a new one, which
initially contains only the current file. The command M-x
filesets-remove-buffer removes the current file from a fileset.

You can also edit the list of filesets directly, with M-x
filesets-edit (or by choosing ‘Edit Filesets’ from the
‘Filesets’ menu). The editing is performed in a Customize buffer
(see Easy Customization). Normally, a fileset is a simple list of
files, but you can also define a fileset as a regular expression
matching file names. Some examples of these more complicated filesets
are shown in the Customize buffer. Remember to select ‘Save for
future sessions’ if you want to use the same filesets in future Emacs
sessions.

You can use the command M-x filesets-open to visit all the
files in a fileset, and M-x filesets-close to close them. Use
M-x filesets-run-cmd to run a shell command on all the files in
a fileset. These commands are also available from the ‘Filesets’
menu, where each existing fileset is represented by a submenu.

See Version Control, for a different concept of “filesets”:
groups of files bundled together for version control operations.
Filesets of that type are unnamed, and do not persist across Emacs
sessions.

19 Using Multiple Buffers

The text you are editing in Emacs resides in an object called a
buffer. Each time you visit a file, a buffer is used to hold
the file’s text. Each time you invoke Dired, a buffer is used to hold
the directory listing. If you send a message with C-x m, a
buffer is used to hold the text of the message. When you ask for a
command’s documentation, that appears in a buffer named *Help*.

Each buffer has a unique name, which can be of any length. When a
buffer is displayed in a window, its name is shown in the mode line
(see Mode Line). The distinction between upper and lower case
matters in buffer names. Most buffers are made by visiting files, and
their names are derived from the files’ names; however, you can also
create an empty buffer with any name you want. A newly started Emacs
has several buffers, including one named *scratch*, which can
be used for evaluating Lisp expressions and is not associated with any
file (see Lisp Interaction).

At any time, one and only one buffer is selected; we call it
the current buffer. We sometimes say that a command operates on
“the buffer”; this really means that it operates on the current
buffer. When there is only one Emacs window, the buffer displayed in
that window is current. When there are multiple windows, the buffer
displayed in the selected window is current. See Windows.

Aside from its textual contents, each buffer records several pieces
of information, such as what file it is visiting (if any), whether it
is modified, and what major mode and minor modes are in effect
(see Modes). These are stored in buffer-local
variables—variables that can have a different value in each buffer.
See Locals.

A buffer’s size cannot be larger than some maximum, which is defined
by the largest buffer position representable by Emacs integers.
This is because Emacs tracks buffer positions using that data type.
For typical 64-bit machines, this maximum buffer size is 2^{61} - 2
bytes, or about 2 EiB. For typical 32-bit machines, the maximum is
usually 2^{29} - 2 bytes, or about 512 MiB. Buffer sizes are
also limited by the amount of memory in the system.

19.1 Creating and Selecting Buffers

Similar, but select buffer in another window
(switch-to-buffer-other-window).

C-x 5 b bufferRET

Similar, but select buffer in a separate frame
(switch-to-buffer-other-frame).

C-x LEFT

Select the previous buffer in the buffer list (previous-buffer).

C-x RIGHT

Select the next buffer in the buffer list (next-buffer).

C-u M-g M-g

C-u M-g g

Read a number n and move to line n in the most recently
selected buffer other than the current buffer.

The C-x b (switch-to-buffer) command reads a buffer
name using the minibuffer. Then it makes that buffer current, and
displays it in the currently-selected window. An empty input
specifies the buffer that was current most recently among those not
now displayed in any window.

While entering the buffer name, you can use the usual completion and
history commands (see Minibuffer). Note that C-x b, and
related commands, use “permissive completion with confirmation” for
minibuffer completion: if you type RET immediately after
completing up to a nonexistent buffer name, Emacs prints
‘[Confirm]’ and you must type a second RET to submit that
buffer name. See Completion Exit, for details.

If you specify a buffer that does not exist, C-x b creates a
new, empty buffer that is not visiting any file, and selects it for
editing. The default value of the variable major-mode
determines the new buffer’s major mode; the default value is
Fundamental mode. See Major Modes. One reason to create a new
buffer is to use it for making temporary notes. If you try to save
it, Emacs asks for the file name to use, and the buffer’s major mode
is re-established taking that file name into account (see Choosing Modes).

For conveniently switching between a few buffers, use the commands
C-x LEFT and C-x RIGHT. C-x LEFT
(previous-buffer) selects the previous buffer (following the
order of most recent selection in the current frame), while C-x
RIGHT (next-buffer) moves through buffers in the reverse
direction.

To select a buffer in a window other than the current one, type
C-x 4 b (switch-to-buffer-other-window). This prompts
for a buffer name using the minibuffer, displays that buffer in
another window, and selects that window.

Similarly, C-x 5 b (switch-to-buffer-other-frame)
prompts for a buffer name, displays that buffer in another frame, and
selects that frame. If the buffer is already being shown in a window
on another frame, Emacs selects that window and frame instead of
creating a new frame.

See Displaying Buffers, for how the C-x 4 b and C-x 5
b commands get the window and/or frame to display in.

In addition, C-x C-f, and any other command for visiting a
file, can also be used to switch to an existing file-visiting buffer.
See Visiting.

C-u M-g M-g, that is goto-line with a plain prefix
argument, reads a number n using the minibuffer, selects the
most recently selected buffer other than the current buffer in another
window, and then moves point to the beginning of line number n
in that buffer. This is mainly useful in a buffer that refers to line
numbers in another buffer: if point is on or just after a number,
goto-line uses that number as the default for n. Note
that prefix arguments other than just C-u behave differently.
C-u 4 M-g M-g goes to line 4 in the current buffer,
without reading a number from the minibuffer. (Remember that M-g
M-g without prefix argument reads a number n and then moves to
line number n in the current buffer. See Moving Point.)

Emacs uses buffer names that start with a space for internal purposes.
It treats these buffers specially in minor ways—for example, by
default they do not record undo information. It is best to avoid using
such buffer names yourself.

19.2 Listing Existing Buffers

C-x C-b

List the existing buffers (list-buffers).

To display a list of existing buffers, type C-x C-b. Each
line in the list shows one buffer’s name, size, major mode and visited file.
The buffers are listed in the order that they were current; the
buffers that were current most recently come first.

‘.’ in the first field of a line indicates that the buffer is
current. ‘%’ indicates a read-only buffer. ‘*’ indicates
that the buffer is “modified”. If several buffers are modified, it
may be time to save some with C-x s (see Save Commands).
Here is an example of a buffer list:

The buffer *Help* was made by a help request (see Help); it
is not visiting any file. The buffer src was made by Dired on
the directory ~/cvs/emacs/src/. You can list only buffers that
are visiting files by giving the command a prefix argument, as in
C-u C-x C-b.

list-buffers omits buffers whose names begin with a space,
unless they visit files: such buffers are used internally by Emacs.

A buffer can be read-only, which means that commands to change
its contents are not allowed. The mode line indicates read-only
buffers with ‘%%’ or ‘%*’ near the left margin. Read-only
buffers are usually made by subsystems such as Dired and Rmail that
have special commands to operate on the text; also by visiting a file
whose access control says you cannot write it.

The command C-x C-q (read-only-mode) makes a read-only
buffer writable, and makes a writable buffer read-only. This works by
setting the variable buffer-read-only, which has a local value
in each buffer and makes the buffer read-only if its value is
non-nil. If you change the option view-read-only to a
non-nil value, making the buffer read-only with C-x C-q
also enables View mode in the buffer (see View Mode).

M-x rename-buffer changes the name of the current buffer. You
specify the new name as a minibuffer argument; there is no default.
If you specify a name that is in use for some other buffer, an error
happens and no renaming is done.

M-x rename-uniquely renames the current buffer to a similar
name with a numeric suffix added to make it both different and unique.
This command does not need an argument. It is useful for creating
multiple shell buffers: if you rename the *shell* buffer, then
do M-x shell again, it makes a new shell buffer named
*shell*; meanwhile, the old shell buffer continues to exist
under its new name. This method is also good for mail buffers,
compilation buffers, and most Emacs features that create special
buffers with particular names. (With some of these features, such as
M-x compile, M-x grep, you need to switch to some other
buffer before using the command again, otherwise it will reuse the
current buffer despite the name change.)

The commands M-x append-to-buffer and M-x insert-buffer
can also be used to copy text from one buffer to another.
See Accumulating Text.

19.4 Killing Buffers

If you continue an Emacs session for a while, you may accumulate a
large number of buffers. You may then find it convenient to kill
the buffers you no longer need. (Some other editors call this
operation close, and talk about “closing the buffer” or
“closing the file” visited in the buffer.) On most operating
systems, killing a buffer releases its space back to the operating
system so that other programs can use it. Here are some commands for
killing buffers:

C-x k bufnameRET

Kill buffer bufname (kill-buffer).

M-x kill-some-buffers

Offer to kill each buffer, one by one.

M-x kill-matching-buffers

Offer to kill all buffers matching a regular expression.

C-x k (kill-buffer) kills one buffer, whose name you
specify in the minibuffer. The default, used if you type just
RET in the minibuffer, is to kill the current buffer. If you
kill the current buffer, another buffer becomes current: one that was
current in the recent past but is not displayed in any window now. If
you ask to kill a file-visiting buffer that is modified, then you must
confirm with yes before the buffer is killed.

The command M-x kill-some-buffers asks about each buffer, one
by one. An answer of y means to kill the buffer, just like
kill-buffer. This command ignores buffers whose names begin
with a space, which are used internally by Emacs.

The command M-x kill-matching-buffers prompts for a regular
expression and kills all buffers whose names match that expression.
See Regexps. Like kill-some-buffers, it asks for
confirmation before each kill. This command normally ignores buffers
whose names begin with a space, which are used internally by Emacs.
To kill internal buffers as well, call kill-matching-buffers
with a prefix argument.

The Buffer Menu feature is also convenient for killing various
buffers. See Several Buffers.

If you want to do something special every time a buffer is killed, you
can add hook functions to the hook kill-buffer-hook (see Hooks).

If you run one Emacs session for a period of days, as many people do,
it can fill up with buffers that you used several days ago. The command
M-x clean-buffer-list is a convenient way to purge them; it kills
all the unmodified buffers that you have not used for a long time. An
ordinary buffer is killed if it has not been displayed for three days;
however, you can specify certain buffers that should never be killed
automatically, and others that should be killed if they have been unused
for a mere hour.

You can also have this buffer purging done for you, once a day,
by enabling Midnight mode. Midnight mode operates each day
at midnight; at that time, it runs clean-buffer-list, or
whichever functions you have placed in the normal hook
midnight-hook (see Hooks). To enable Midnight mode, use
the Customization buffer to set the variable midnight-mode to
t. See Easy Customization.

19.5 Operating on Several Buffers

M-x buffer-menu

Begin editing a buffer listing all Emacs buffers.

M-x buffer-menu-other-window.

Similar, but do it in another window.

The Buffer Menu opened by C-x C-b (see List Buffers)
does not merely list buffers. It also allows you to perform various
operations on buffers, through an interface similar to Dired
(see Dired). You can save buffers, kill them (here called
deleting them, for consistency with Dired), or display them.

To use the Buffer Menu, type C-x C-b and switch to the window
displaying the *Buffer List* buffer. You can also type
M-x buffer-menu to open the Buffer Menu in the selected window.
Alternatively, the command M-x buffer-menu-other-window opens
the Buffer Menu in another window, and selects that window.

The Buffer Menu is a read-only buffer, and can be changed only
through the special commands described in this section. The usual
cursor motion commands can be used in this buffer. The following
commands apply to the buffer described on the current line:

d

Flag the buffer for deletion (killing), then move point to the next
line (Buffer-menu-delete). The deletion flag is indicated by
the character ‘D’ on the line, before the buffer name. The
deletion occurs only when you type the x command (see below).

C-d

Like d, but move point up instead of down
(Buffer-menu-delete-backwards).

s

Flag the buffer for saving (Buffer-menu-save). The save flag
is indicated by the character ‘S’ on the line, before the buffer
name. The saving occurs only when you type x. You may request
both saving and deletion for the same buffer.

x

Perform all flagged deletions and saves (Buffer-menu-execute).

u

Remove all flags from the current line, and move down
(Buffer-menu-unmark).

DEL

Move to the previous line and remove all flags on that line
(Buffer-menu-backup-unmark).

The commands for adding or removing flags, d, C-d, s
and u, all accept a numeric argument as a repeat count.

The following commands operate immediately on the buffer listed on
the current line. They also accept a numeric argument as a repeat
count.

~

Mark the buffer as unmodified (Buffer-menu-not-modified).
See Save Commands.

Visit the buffer as a tags table
(Buffer-menu-visit-tags-table). See Select Tags Table.

The following commands are used to select another buffer or buffers:

q

Quit the Buffer Menu (quit-window). The most recent formerly
visible buffer is displayed in its place.

RET

f

Select this line’s buffer, replacing the *Buffer List* buffer
in its window (Buffer-menu-this-window).

o

Select this line’s buffer in another window, as if by C-x 4 b,
leaving *Buffer List* visible
(Buffer-menu-other-window).

C-o

Display this line’s buffer in another window, without selecting it
(Buffer-menu-switch-other-window).

1

Select this line’s buffer in a full-frame window
(Buffer-menu-1-window).

2

Set up two windows on the current frame, with this line’s buffer
selected in one, and a previously current buffer (aside from
*Buffer List*) in the other (Buffer-menu-2-window).

b

Bury this line’s buffer (Buffer-menu-bury).

m

Mark this line’s buffer to be displayed in another window if you exit
with the v command (Buffer-menu-mark). The display flag
is indicated by the character ‘>’ at the beginning of the line.
(A single buffer may not have both deletion and display flags.)

v

Select this line’s buffer, and also display in other windows any
buffers flagged with the m command (Buffer-menu-select).
If you have not flagged any buffers, this command is equivalent to
1.

The following commands affect the entire buffer list:

S

Sort the Buffer Menu entries according to their values in the column
at point. With a numeric prefix argument n, sort according to
the n-th column (tabulated-list-sort).

T

Delete, or reinsert, lines for non-file buffers
Buffer-menu-toggle-files-only). This command toggles the
inclusion of such buffers in the buffer list.

Normally, the buffer *Buffer List* is not updated
automatically when buffers are created and killed; its contents are
just text. If you have created, deleted or renamed buffers, the way
to update *Buffer List* to show what you have done is to type
g (revert-buffer). You can make this happen regularly
every auto-revert-interval seconds if you enable Auto Revert
mode in this buffer, as long as it is not marked modified. Global
Auto Revert mode applies to the *Buffer List* buffer only if
global-auto-revert-non-file-buffers is non-nil.
See global-auto-revert-non-file-buffers, for details.

19.6 Indirect Buffers

An indirect buffer shares the text of some other buffer, which
is called the base buffer of the indirect buffer. In some ways it
is a buffer analogue of a symbolic link between files.

M-x make-indirect-buffer RETbase-bufferRETindirect-nameRET

Create an indirect buffer named indirect-name with base buffer
base-buffer.

M-x clone-indirect-buffer RET

Create an indirect buffer that is a twin copy of the current buffer.

C-x 4 c

Create an indirect buffer that is a twin copy of the current buffer, and
select it in another window (clone-indirect-buffer-other-window).

The text of the indirect buffer is always identical to the text of its
base buffer; changes made by editing either one are visible immediately
in the other. But in all other respects, the indirect buffer and its
base buffer are completely separate. They can have different names,
different values of point, different narrowing, different markers,
different major modes, and different local variables.

An indirect buffer cannot visit a file, but its base buffer can. If
you try to save the indirect buffer, that actually works by saving the
base buffer. Killing the base buffer effectively kills the indirect
buffer, but killing an indirect buffer has no effect on its base buffer.

One way to use indirect buffers is to display multiple views of an
outline. See Outline Views.

A quick and handy way to make an indirect buffer is with the command
M-x clone-indirect-buffer. It creates and selects an indirect
buffer whose base buffer is the current buffer. With a numeric
argument, it prompts for the name of the indirect buffer; otherwise it
uses the name of the current buffer, with a ‘<n>’ suffix
added. C-x 4 c (clone-indirect-buffer-other-window)
works like M-x clone-indirect-buffer, but it selects the new
buffer in another window. These functions run the hook
clone-indirect-buffer-hook after creating the indirect buffer.

The more general way to make an indirect buffer is with the command
M-x make-indirect-buffer. It creates an indirect buffer
named indirect-name from a buffer base-buffer, prompting for
both using the minibuffer.

19.7.1 Making Buffer Names Unique

When several buffers visit identically-named files, Emacs must give
the buffers distinct names. The default method adds a suffix based on
the names of the directories that contain the files. For example, if
you visit files /foo/bar/mumble/name and
/baz/quux/mumble/name at the same time, their buffers will be
named ‘name<bar/mumble>’ and ‘name<quux/mumble>’, respectively.
Emacs adds as many directory parts as are needed to make a unique name.

You can choose from several different styles for constructing unique
buffer names, by customizing the option uniquify-buffer-name-style.

The forward naming method includes part of the file’s
directory name at the beginning of the buffer name; using this method,
buffers visiting the files /u/rms/tmp/Makefile and
/usr/projects/zaphod/Makefile would be named
‘tmp/Makefile’ and ‘zaphod/Makefile’.

In contrast, the post-forward naming method would call the
buffers ‘Makefile|tmp’ and ‘Makefile|zaphod’. The default
method post-forward-angle-brackets is like post-forward,
except that it encloses the unique path in angle brackets. The
reverse naming method would call them ‘Makefile\tmp’ and
‘Makefile\zaphod’. The nontrivial difference between
post-forward and reverse occurs when just one directory
name is not enough to distinguish two files; then reverse puts
the directory names in reverse order, so that /top/middle/file
becomes ‘file\middle\top’, while post-forward puts them in
forward order after the file name, as in ‘file|top/middle’. If
uniquify-buffer-name-style is set to nil, the buffer
names simply get ‘<2>’, ‘<3>’, etc. appended.

Which rule to follow for putting the directory names in the buffer
name is not very important if you are going to look at the
buffer names before you type one. But as an experienced user, if you
know the rule, you won’t have to look. And then you may find that one
rule or another is easier for you to remember and apply quickly.

19.7.2 Fast minibuffer selection

Icomplete global minor mode provides a convenient way to quickly select an
element among the possible completions in a minibuffer. When enabled, typing
in the minibuffer continuously displays a list of possible completions that
match the string you have typed.

At any time, you can type C-j to select the first completion in
the list. So the way to select a particular completion is to make it the
first in the list. There are two ways to do this. You can type more
of the completion name and thus narrow down the list, excluding unwanted
completions above the desired one. Alternatively, you can use C-.
and C-, to rotate the list until the desired buffer is first.

M-TAB will select the first completion in the list, like
C-j but without exiting the minibuffer, so you can edit it
further. This is typically used when entering a file name, where
M-TAB can be used a few times to descend in the hierarchy
of directories.

19.7.3 Customizing Buffer Menus

M-x bs-show

Make a list of buffers similarly to M-x list-buffers but
customizable.

M-x bs-show pops up a buffer list similar to the one normally
displayed by C-x C-b but which you can customize. If you prefer
this to the usual buffer list, you can bind this command to C-x
C-b. To customize this buffer list, use the bs Custom group
(see Easy Customization).

MSB global minor mode (“MSB” stands for “mouse select buffer”)
provides a different and customizable mouse buffer menu which you may
prefer. It replaces the bindings of mouse-buffer-menu,
normally on C-Down-Mouse-1, and the menu bar buffer menu. You
can customize the menu in the msb Custom group.

20 Multiple Windows

Emacs can split a frame into two or many windows. Multiple windows
can display parts of different buffers, or different parts of one
buffer. Multiple frames always imply multiple windows, because each
frame has its own set of windows. Each window belongs to one and only
one frame.

20.1 Concepts of Emacs Windows

Each Emacs window displays one Emacs buffer at any time. A single
buffer may appear in more than one window; if it does, any changes in
its text are displayed in all the windows where it appears. But these
windows can show different parts of the buffer, because each window
has its own value of point.

At any time, one Emacs window is the selected window; the
buffer this window is displaying is the current buffer. On graphical
displays, the point is indicated by a solid blinking cursor in the
selected window, and by a hollow box in non-selected windows. On text
terminals, the cursor is drawn only in the selected window.
See Cursor Display.

Commands to move point affect the value of point for the selected
Emacs window only. They do not change the value of point in other
Emacs windows, even those showing the same buffer. The same is true
for buffer-switching commands such as C-x b; they do not affect
other windows at all. However, there are other commands such as
C-x 4 b that select a different window and switch buffers in it.
Also, all commands that display information in a window, including
(for example) C-h f (describe-function) and C-x C-b
(list-buffers), work by switching buffers in a nonselected
window without affecting the selected window.

When multiple windows show the same buffer, they can have different
regions, because they can have different values of point. However,
they all have the same value for the mark, because each buffer has
only one mark position.

Each window has its own mode line, which displays the buffer name,
modification status and major and minor modes of the buffer that is
displayed in the window. The selected window’s mode line appears in a
different color. See Mode Line, for details.

20.2 Splitting Windows

Split the selected window into two windows, one above the other
(split-window-below).

C-x 3

Split the selected window into two windows, positioned side by side
(split-window-right).

C-Mouse-2

In the mode line of a window, split that window.

C-x 2 (split-window-below) splits the selected window
into two windows, one above the other. After splitting, the selected
window is the upper one, and the newly split-off window is below.
Both windows have the same value of point as before, and display the
same portion of the buffer (or as close to it as possible). If
necessary, the windows are scrolled to keep point on-screen. By
default, the two windows each get half the height of the original
window. A positive numeric argument specifies how many lines to give
to the top window; a negative numeric argument specifies how many
lines to give to the bottom window.

If you change the variable split-window-keep-point to
nil, C-x 2 instead adjusts the portion of the buffer
displayed by the two windows, as well as the value of point in each
window, in order to keep the text on the screen as close as possible
to what it was before; furthermore, if point was in the lower half of
the original window, the bottom window is selected instead of the
upper one.

C-x 3 (split-window-right) splits the selected window
into two side-by-side windows. The left window is the selected one;
the right window displays the same portion of the same buffer, and has
the same value of point. A positive numeric argument specifies how
many columns to give the left window; a negative numeric argument
specifies how many columns to give the right window.

When you split a window with C-x 3, each resulting window
occupies less than the full width of the frame. If it becomes too
narrow, the buffer may be difficult to read if continuation lines are
in use (see Continuation Lines). Therefore, Emacs automatically
switches to line truncation if the window width becomes narrower than
50 columns. This truncation occurs regardless of the value of the
variable truncate-lines (see Line Truncation); it is
instead controlled by the variable
truncate-partial-width-windows. If the value of this variable
is a positive integer (the default is 50), that specifies the minimum
width for a partial-width window before automatic line truncation
occurs; if the value is nil, automatic line truncation is
disabled; and for any other non-nil value, Emacs truncates
lines in every partial-width window regardless of its width.

On text terminals, side-by-side windows are separated by a vertical
divider which is drawn using the vertical-border face.

If you click C-Mouse-2 in the mode line of a window, that
splits the window, putting a vertical divider where you click.
Depending on how Emacs is compiled, you can also split a window by
clicking C-Mouse-2 in the scroll bar, which puts a horizontal
divider where you click (this feature does not work when Emacs uses
GTK+ scroll bars).

By default, when you split a window, Emacs gives each of the
resulting windows dimensions that are an integral multiple of the
default font size of the frame. That might subdivide the screen
estate unevenly between the resulting windows. If you set the
variable window-resize-pixelwise to a non-nil value,
Emacs will give each window the same number of pixels (give or take
one pixel if the initial dimension was an odd number of pixels). Note
that when a frame’s pixel size is not a multiple of the frame’s
character size, at least one window may get resized pixelwise even if
this option is nil.

20.3 Using Other Windows

Mouse-1, in the text area of a window, selects the window and
moves point to the position clicked. Clicking in the mode line
selects the window without moving point in it.

With the keyboard, you can switch windows by typing C-x o
(other-window). That is an o, for “other”, not a zero.
When there are more than two windows, this command moves through all the
windows in a cyclic order, generally top to bottom and left to right.
After the rightmost and bottommost window, it goes back to the one at
the upper left corner. A numeric argument means to move several steps
in the cyclic order of windows. A negative argument moves around the
cycle in the opposite order. When the minibuffer is active, the
minibuffer is the last window in the cycle; you can switch from the
minibuffer window to one of the other windows, and later switch back and
finish supplying the minibuffer argument that is requested.
See Minibuffer Edit.

The usual scrolling commands (see Display) apply to the selected
window only, but there is one command to scroll the next window.
C-M-v (scroll-other-window) scrolls the window that
C-x o would select. It takes arguments, positive and negative,
like C-v. (In the minibuffer, C-M-v scrolls the help
window associated with the minibuffer, if any, rather than the next
window in the standard cyclic order; see Minibuffer Edit.)

If you set mouse-autoselect-window to a non-nil value,
moving the mouse over a different window selects that window. This
feature is off by default.

20.4 Displaying in Another Window

C-x 4 is a prefix key for a variety of commands that switch to
a buffer in a different window—either another existing window, or a
new window created by splitting the selected window. See Window Choice, for how Emacs picks or creates the window to use.

20.5 Deleting and Rearranging Windows

Delete all windows in the selected frame except the selected window
(delete-other-windows).

C-x 4 0

Delete the selected window and kill the buffer that was showing in it
(kill-buffer-and-window). The last character in this key
sequence is a zero.

C-x ^

Make selected window taller (enlarge-window).

C-x }

Make selected window wider (enlarge-window-horizontally).

C-x {

Make selected window narrower (shrink-window-horizontally).

C-x -

Shrink this window if its buffer doesn’t need so many lines
(shrink-window-if-larger-than-buffer).

C-x +

Make all windows the same height (balance-windows).

To delete the selected window, type C-x 0
(delete-window). (That is a zero.) Once a window is deleted,
the space that it occupied is given to an adjacent window (but not the
minibuffer window, even if that is active at the time). Deleting the
window has no effect on the buffer it used to display; the buffer
continues to exist, and you can still switch to it with C-x b.

C-x 4 0 (kill-buffer-and-window) is a stronger command
than C-x 0; it kills the current buffer and then deletes the
selected window.

C-x 1 (delete-other-windows) deletes all the windows,
except the selected one; the selected window expands to use the
whole frame. (This command cannot be used while the minibuffer window
is active; attempting to do so signals an error.)

The command C-x ^ (enlarge-window) makes the selected
window one line taller, taking space from a vertically adjacent window
without changing the height of the frame. With a positive numeric
argument, this command increases the window height by that many lines;
with a negative argument, it reduces the height by that many lines.
If there are no vertically adjacent windows (i.e., the window is at the
full frame height), that signals an error. The command also signals
an error if you attempt to reduce the height of any window below a
certain minimum number of lines, specified by the variable
window-min-height (the default is 4).

Similarly, C-x } (enlarge-window-horizontally) makes
the selected window wider, and C-x {
(shrink-window-horizontally) makes it narrower. These commands
signal an error if you attempt to reduce the width of any window below
a certain minimum number of columns, specified by the variable
window-min-width (the default is 10).

C-x - (shrink-window-if-larger-than-buffer) reduces the
height of the selected window, if it is taller than necessary to show
the whole text of the buffer it is displaying. It gives the extra
lines to other windows in the frame.

You can also use C-x + (balance-windows) to even out the
heights of all the windows in the selected frame.

Mouse clicks on the mode line provide another way to change window
heights and to delete windows. See Mode Line Mouse.

20.6 Displaying a Buffer in a Window

It is a common Emacs operation to display or “pop up” some buffer
in response to a user command. There are several different ways in
which commands do this.

Many commands, like C-x C-f (find-file), display the
buffer by “taking over” the selected window, expecting that the
user’s attention will be diverted to that buffer. These commands
usually work by calling switch-to-buffer internally
(see Select Buffer).

Some commands try to display “intelligently”, trying not to take
over the selected window, e.g., by splitting off a new window and
displaying the desired buffer there. Such commands, which include the
various help commands (see Help), work by calling
display-buffer internally. See Window Choice, for details.

Other commands do the same as display-buffer, and
additionally select the displaying window so that you can begin
editing its buffer. The command C-x ` (next-error) is
one example (see Compilation Mode). Such commands work by calling
the function pop-to-buffer internally. See Switching to a Buffer in a Window in The Emacs Lisp
Reference Manual.

Commands with names ending in -other-window behave like
display-buffer, except that they never display in the selected
window. Several of these commands are bound in the C-x 4 prefix
key (see Pop Up Window).

Commands with names ending in -other-frame behave like
display-buffer, except that they (i) never display in the
selected window and (ii) prefer to create a new frame to display the
desired buffer instead of splitting a window—as though the variable
pop-up-frames is set to t (see Window Choice).
Several of these commands are bound in the C-x 5 prefix key.

20.6.1 How display-buffer works

The display-buffer command (as well as commands that call it
internally) chooses a window to display by following the steps given
below. See Choosing a Window for Display in The Emacs Lisp Reference Manual, for details about how to alter this
sequence of steps.

First, check if the buffer should be displayed in the selected window
regardless of other considerations. You can tell Emacs to do this by
adding the desired buffer’s name to the list
same-window-buffer-names, or adding a matching regular
expression to the list same-window-regexps. By default, these
variables are nil, so this step is skipped.

Otherwise, if the buffer is already displayed in an existing window,
“reuse” that window. Normally, only windows on the selected frame
are considered, but windows on other frames are also reusable if you
change pop-up-frames (see below) to t.

Otherwise, optionally create a new frame and display the buffer there.
By default, this step is skipped. To enable it, change the variable
pop-up-frames to a non-nil value. The special value
graphic-only means to do this only on graphical displays.

Otherwise, try to create a new window by splitting the selected
window, and display the buffer in that new window.

The split can be either vertical or horizontal, depending on the
variables split-height-threshold and
split-width-threshold. These variables should have integer
values. If split-height-threshold is smaller than the selected
window’s height, the split puts the new window below. Otherwise, if
split-width-threshold is smaller than the window’s width, the
split puts the new window on the right. If neither condition holds,
Emacs tries to split so that the new window is below—but only if the
window was not split before (to avoid excessive splitting).

Otherwise, display the buffer in an existing window on the selected
frame.

If all the above methods fail for whatever reason, create a new frame
and display the buffer there.

20.7 Convenience Features for Window Handling

Winner mode is a global minor mode that records the changes in the
window configuration (i.e., how the frames are partitioned into
windows), so that you can “undo” them. You can toggle Winner mode
with M-x winner-mode, or by customizing the variable
winner-mode. When the mode is enabled, C-c left
(winner-undo) undoes the last window configuration change. If
you change your mind while undoing, you can redo the changes you had
undone using C-c right (M-x winner-redo).

Follow mode (M-x follow-mode) synchronizes several windows on
the same buffer so that they always display adjacent sections of that
buffer. See Follow Mode.

The Windmove package defines commands for moving directionally
between neighboring windows in a frame. M-x windmove-right
selects the window immediately to the right of the currently selected
one, and similarly for the “left”, “up”, and “down”
counterparts. M-x windmove-default-keybindings binds these
commands to S-right etc.; doing so disables shift selection for
those keys (see Shift Selection).

The command M-x compare-windows lets you compare the text
shown in different windows. See Comparing Files.

Scroll All mode (M-x scroll-all-mode) is a global minor mode
that causes scrolling commands and point motion commands to apply to
every single window.

21 Frames and Graphical Displays

When Emacs is started on a graphical display, e.g., on the X Window
System, it occupies a graphical system-level “window”. In this
manual, we call this a frame, reserving the word “window” for
the part of the frame used for displaying a buffer. A frame initially
contains one window, but it can be subdivided into multiple windows
(see Windows). A frame normally also contains a menu bar, tool
bar, and echo area.

You can also create additional frames (see Creating Frames).
All frames created in the same Emacs session have access to the same
underlying buffers and other data. For instance, if a buffer is being
shown in more than one frame, any changes made to it in one frame show
up immediately in the other frames too.

Typing C-x C-c closes all the frames on the current display,
and ends the Emacs session if it has no frames open on any other
displays (see Exiting). To close just the selected frame, type
C-x 5 0 (that is zero, not o).

This chapter describes Emacs features specific to graphical displays
(particularly mouse commands), and features for managing multiple
frames. On text terminals, many of these features are unavailable.
However, it is still possible to create multiple “frames” on text
terminals; such frames are displayed one at a time, filling the entire
terminal screen (see Non-Window Terminals). It is also possible
to use the mouse on some text terminals (see Text-Only Mouse, for
doing so on GNU and Unix systems; and
see MS-DOS Mouse,
for doing so on MS-DOS). Menus are supported on all text terminals.

21.1 Mouse Commands for Editing

Activate the region around the text selected by dragging, and put the
text in the primary selection (mouse-set-region).

Mouse-2

Move point to where you click, and insert the contents of the primary
selection there (mouse-yank-primary).

Mouse-3

If the region is active, move the nearer end of the region to the
click position; otherwise, set mark at the current value of point and
point at the click position. Save the resulting region in the kill
ring; on a second click, kill it (mouse-save-then-kill).

The most basic mouse command is mouse-set-point, which is
invoked by clicking with the left mouse button, Mouse-1, in the
text area of a window. This moves point to the position where you
clicked. If that window was not the selected window, it becomes the
selected window.

Normally, if the frame you clicked in was not the selected frame, it
is made the selected frame, in addition to selecting the window and
setting the cursor. On the X Window System, you can change this by
setting the variable x-mouse-click-focus-ignore-position to
t. In that case, the initial click on an unselected frame just
selects the frame, without doing anything else; clicking again selects
the window and sets the cursor position.

Holding down Mouse-1 and “dragging” the mouse over a stretch
of text activates the region around that text
(mouse-set-region), placing the mark where you started holding
down the mouse button, and point where you release it (see Mark).
In addition, the text in the region becomes the primary selection
(see Primary Selection).

If you change the variable mouse-drag-copy-region to a
non-nil value, dragging the mouse over a stretch of text also
adds the text to the kill ring. The default is nil.

If you move the mouse off the top or bottom of the window while
dragging, the window scrolls at a steady rate until you move the mouse
back into the window. This way, you can select regions that don’t fit
entirely on the screen. The number of lines scrolled per step depends
on how far away from the window edge the mouse has gone; the variable
mouse-scroll-min-lines specifies a minimum step size.

Clicking with the middle mouse button, Mouse-2, moves point to
the position where you clicked and inserts the contents of the primary
selection (mouse-yank-primary). See Primary Selection.
This behavior is consistent with other X applications. Alternatively,
you can rebind Mouse-2 to mouse-yank-at-click, which
performs a yank at the position you click.

If you change the variable mouse-yank-at-point to a
non-nil value, Mouse-2 does not move point; it inserts
the text at point, regardless of where you clicked or even which of
the frame’s windows you clicked on. This variable affects both
mouse-yank-primary and mouse-yank-at-click.

Clicking with the right mouse button, Mouse-3, runs the
command mouse-save-then-kill. This performs several actions
depending on where you click and the status of the region:

If no region is active, clicking Mouse-3 activates the region,
placing the mark where point was and point at the clicked position.

If a region is active, clicking Mouse-3 adjusts the nearer end
of the region by moving it to the clicked position. The adjusted
region’s text is copied to the kill ring; if the text in the original
region was already on the kill ring, it replaces it there.

If you originally specified the region using a double or triple
Mouse-1, so that the region is defined to consist of entire
words or lines (see Word and Line Mouse), then adjusting the
region with Mouse-3 also proceeds by entire words or lines.

If you use Mouse-3 a second time consecutively, at the same
place, that kills the region already selected. Thus, the simplest way
to kill text with the mouse is to click Mouse-1 at one end, then
click Mouse-3 twice at the other end. To copy the text into the
kill ring without deleting it from the buffer, press Mouse-3
just once—or just drag across the text with Mouse-1. Then you
can copy it elsewhere by yanking it.

The mouse-save-then-kill command also obeys the variable
mouse-drag-copy-region (described above). If the value is
non-nil, then whenever the command sets or adjusts the active
region, the text in the region is also added to the kill ring. If the
latest kill ring entry had been added the same way, that entry is
replaced rather than making a new entry.

Whenever you set the region using any of the mouse commands
described above, the mark will be deactivated by any subsequent
unshifted cursor motion command, in addition to the usual ways of
deactivating the mark. See Shift Selection.

Some mice have a “wheel” which can be used for scrolling. Emacs
supports scrolling windows with the mouse wheel, by default, on most
graphical displays. To toggle this feature, use M-x
mouse-wheel-mode. The variables mouse-wheel-follow-mouse and
mouse-wheel-scroll-amount determine where and by how much
buffers are scrolled. The variable
mouse-wheel-progressive-speed determines whether the scroll
speed is linked to how fast you move the wheel.

21.2 Mouse Commands for Words and Lines

These variants of Mouse-1 select entire words or lines at a
time. Emacs activates the region around the selected text, which is
also copied to the kill ring.

Double-Mouse-1

Select the text around the word which you click on.

Double-clicking on a character with “symbol” syntax (such as
underscore, in C mode) selects the symbol surrounding that character.
Double-clicking on a character with open- or close-parenthesis syntax
selects the parenthetical grouping which that character starts or
ends. Double-clicking on a character with string-delimiter syntax
(such as a single-quote or double-quote in C) selects the string
constant (Emacs uses heuristics to figure out whether that character
is the beginning or the end of it).

21.3 Following References with the Mouse

Some Emacs buffers include buttons, or hyperlinks:
pieces of text that perform some action (e.g., following a reference)
when activated (e.g., by clicking on them). Usually, a button’s text
is visually highlighted: it is underlined, or a box is drawn around
it. If you move the mouse over a button, the shape of the mouse
cursor changes and the button lights up. If you change the variable
mouse-highlight to nil, Emacs disables this
highlighting.

You can activate a button by moving point to it and typing
RET, or by clicking either Mouse-1 or Mouse-2 on the
button. For example, in a Dired buffer, each file name is a button;
activating it causes Emacs to visit that file (see Dired). In a
*Compilation* buffer, each error message is a button, and
activating it visits the source code for that error
(see Compilation).

Although clicking Mouse-1 on a button usually activates the
button, if you hold the mouse button down for a period of time before
releasing it (specifically, for more than 450 milliseconds), then
Emacs moves point where you clicked, without activating the button.
In this way, you can use the mouse to move point over a button without
activating it. Dragging the mouse over or onto a button has its usual
behavior of setting the region, and does not activate the button.

You can change how Mouse-1 applies to buttons by customizing
the variable mouse-1-click-follows-link. If the value is a
positive integer, that determines how long you need to hold the mouse
button down for, in milliseconds, to cancel button activation; the
default is 450, as described in the previous paragraph. If the value
is nil, Mouse-1 just sets point where you clicked, and
does not activate buttons. If the value is double, double
clicks activate buttons but single clicks just set point.

Normally, Mouse-1 on a button activates the button even if it
is in a non-selected window. If you change the variable
mouse-1-click-in-non-selected-windows to nil,
Mouse-1 on a button in an unselected window moves point to the
clicked position and selects that window, without activating the
button.

This menu contains entries for examining faces and other text
properties, and well as for setting them (the latter is mainly useful
when editing enriched text; see Enriched Text).

C-Mouse-3

This menu is mode-specific. For most modes if Menu-bar mode is on,
this menu has the same items as all the mode-specific menu-bar menus
put together. Some modes may specify a different menu for this
button. If Menu Bar mode is off, this menu contains all the items
which would be present in the menu bar—not just the mode-specific
ones—so that you can access them without having to display the menu
bar.

S-Mouse-1

This menu is for changing the default face within the window’s buffer.
See Text Scale.

Some graphical applications use Mouse-3 for a mode-specific
menu. If you prefer Mouse-3 in Emacs to bring up such a menu
instead of running the mouse-save-then-kill command, rebind
Mouse-3 by adding the following line to your init file
(see Init Rebinding):

21.5 Mode Line Mouse Commands

You can use mouse clicks on window mode lines to select and manipulate
windows.

Some areas of the mode line, such as the buffer name, and major and minor
mode names, have their own special mouse bindings. These areas are
highlighted when you hold the mouse over them, and information about
the special bindings will be displayed (see Tooltips). This
section’s commands do not apply in those areas.

Mouse-1

Mouse-1 on a mode line selects the window it belongs to. By
dragging Mouse-1 on the mode line, you can move it, thus
changing the height of the windows above and below. Changing heights
with the mouse in this way never deletes windows, it just refuses to
make any window smaller than the minimum height.

Mouse-2

Mouse-2 on a mode line expands that window to fill its frame.

Mouse-3

Mouse-3 on a mode line deletes the window it belongs to. If the
frame has only one window, it does nothing.

C-Mouse-2

C-Mouse-2 on a mode line splits that window, producing two
side-by-side windows with the boundary running through the click
position (see Split Window).

Furthermore, by clicking and dragging Mouse-1 on the divider
between two side-by-side mode lines, you can move the vertical
boundary to the left or right.

Note that resizing windows is affected by the value of
window-resize-pixelwise, see Split Window.

21.6 Creating Frames

The prefix key C-x 5 is analogous to C-x 4. Whereas
each C-x 4 command pops up a buffer in a different window in the
selected frame (see Pop Up Window), the C-x 5 commands use a
different frame. If an existing visible or iconified (“minimized”)
frame already displays the requested buffer, that frame is raised and
deiconified (“un-minimized”); otherwise, a new frame is created on
the current display terminal.

The various C-x 5 commands differ in how they find or create the
buffer to select:

C-x 5 2

Create a new frame (make-frame-command).

C-x 5 b bufnameRET

Select buffer bufname in another frame. This runs
switch-to-buffer-other-frame.

C-x 5 f filenameRET

Visit file filename and select its buffer in another frame. This
runs find-file-other-frame. See Visiting.

C-x 5 d directoryRET

Select a Dired buffer for directory directory in another frame.
This runs dired-other-frame. See Dired.

C-x 5 m

Start composing a mail message in another frame. This runs
mail-other-frame. It is the other-frame variant of C-x m.
See Sending Mail.

C-x 5 .

Find a tag in the current tag table in another frame. This runs
find-tag-other-frame, the multiple-frame variant of M-..
See Tags.

C-x 5 r filenameRET

Visit file filename read-only, and select its buffer in another
frame. This runs find-file-read-only-other-frame.
See Visiting.

You can control the appearance and behavior of the newly-created
frames by specifying frame parameters. See Frame Parameters.

Select another frame, and raise it. If you repeat this command, it
cycles through all the frames on your terminal.

C-x 5 1

Delete all frames on the current terminal, except the selected one.

M-<F10>

Toggle the maximization state of the current frame. When a frame is
maximized, it fills the screen.

<F11>

Toggle fullscreen mode for the current frame. (The difference
between “fullscreen” and “maximized” is normally that the former
hides window manager decorations, giving slightly more screen space to
Emacs itself.)

Note that with some window managers you may have to customize the
variable frame-resize-pixelwise to a non-nil value in
order to make a frame truly “maximized” or “fullscreen”. This
variable, when set to a non-nil value, in general allows
resizing frames at pixel resolution, rather than in integral multiples
of lines and columns.

The C-x 5 0 (delete-frame) command deletes the selected
frame. However, it will refuse to delete the last frame in an Emacs
session, to prevent you from losing the ability to interact with the
Emacs session. Note that when Emacs is run as a daemon (see Emacs Server), there is always a “virtual frame” that remains after all
the ordinary, interactive frames are deleted. In this case, C-x
5 0 can delete the last interactive frame; you can use
emacsclient to reconnect to the Emacs session.

The C-x 5 1 (delete-other-frames) command deletes all
other frames on the current terminal (this terminal refers to either a
graphical display, or a text terminal; see Non-Window Terminals).
If the Emacs session has frames open on other graphical displays or
text terminals, those are not deleted.

The C-x 5 o (other-frame) command selects the next
frame on the current terminal. If you are using Emacs on the X Window
System with a window manager that selects (or gives focus to)
whatever frame the mouse cursor is over, you have to change the
variable focus-follows-mouse to t in order for this
command to work properly. Then invoking C-x 5 o will also warp
the mouse cursor to the chosen frame.

21.8 Fonts

By default, Emacs displays text on graphical displays using a
10-point monospace font. There are several different ways to specify
a different font:

Click on ‘Set Default Font’ in the ‘Options’ menu. This
makes the selected font the default on all existing graphical frames.
To save this for future sessions, click on ‘Save Options’ in the
‘Options’ menu.

Add a line to your init file, modifying the variable
default-frame-alist to specify the font parameter
(see Frame Parameters), like this:

(add-to-list 'default-frame-alist
'(font . "DejaVu Sans Mono-10"))

This makes the font the default on all graphical frames created after
restarting Emacs with that init file.

You must restart X, or use the xrdb command, for the X
resources file to take effect. See Resources. Do not quote
font names in X resource files.

If you are running Emacs on the GNOME desktop, you can tell Emacs to
use the default system font by setting the variable
font-use-system-font to t (the default is nil).
For this to work, Emacs must have been compiled with Gconf support.

To check what font you’re currently using, the C-u C-x =
command can be helpful. It describes the character at point, and
names the font that it’s rendered in.

On X, there are four different ways to express a “font name”. The
first is to use a Fontconfig pattern. Fontconfig patterns have
the following form:

fontname[-fontsize][:name1=values1][:name2=values2]...

Within this format, any of the elements in braces may be omitted.
Here, fontname is the family name of the font, such as
‘Monospace’ or ‘DejaVu Sans Mono’; fontsize is the
point size of the font (one printer’s point is about 1/72
of an inch); and the ‘name=values’ entries specify
settings such as the slant and weight of the font. Each values
may be a single value, or a list of values separated by commas. In
addition, some property values are valid with only one kind of
property name, in which case the ‘name=’ part may be
omitted.

Here is a list of common font properties:

‘slant’

One of ‘italic’, ‘oblique’, or ‘roman’.

‘weight’

One of ‘light’, ‘medium’, ‘demibold’, ‘bold’ or
‘black’.

‘style’

Some fonts define special styles which are a combination of slant and
weight. For instance, ‘Dejavu Sans’ defines the ‘book’
style, which overrides the slant and weight properties.

The second way to specify a font is to use a GTK font pattern.
These have the syntax

fontname [properties] [fontsize]

where fontname is the family name, properties is a list of
property values separated by spaces, and fontsize is the point
size. The properties that you may specify for GTK font patterns are
as follows:

Slant properties: ‘Italic’ or ‘Oblique’. If omitted, the
default (roman) slant is implied.

Width properties: ‘Semi-Condensed’ or ‘Condensed’. If
omitted, a default width is used.

Here are some examples of GTK font patterns:

Monospace 12
Monospace Bold Italic 12

The third way to specify a font is to use an XLFD (X
Logical Font Description). This is the traditional method for
specifying fonts under X. Each XLFD consists of fourteen words or
numbers, separated by dashes, like this:

-misc-fixed-medium-r-semicondensed--13-*-*-*-c-60-iso8859-1

A wildcard character (‘*’) in an XLFD matches any sequence of
characters (including none), and ‘?’ matches any single
character. However, matching is implementation-dependent, and can be
inaccurate when wildcards match dashes in a long name. For reliable
results, supply all 14 dashes and use wildcards only within a field.
Case is insignificant in an XLFD. The syntax for an XLFD is as
follows:

The font width—normally ‘normal’, ‘condensed’,
‘semicondensed’, or ‘extended’. Some font names support
other values.

style

An optional additional style name. Usually it is empty—most XLFDs
have two hyphens in a row at this point.

pixels

The font height, in pixels.

height

The font height on the screen, measured in tenths of a printer’s
point. This is the point size of the font, times ten. For a given
vertical resolution, height and pixels are proportional;
therefore, it is common to specify just one of them and use ‘*’
for the other.

horiz

The horizontal resolution, in pixels per inch, of the screen for which
the font is intended.

vert

The vertical resolution, in pixels per inch, of the screen for which
the font is intended. Normally the resolution of the fonts on your
system is the right value for your screen; therefore, you normally
specify ‘*’ for this and horiz.

spacing

This is ‘m’ (monospace), ‘p’ (proportional) or ‘c’
(character cell).

width

The average character width, in pixels, multiplied by ten.

registry

encoding

The X font character set that the font depicts. (X font character
sets are not the same as Emacs character sets, but they are similar.)
You can use the xfontsel program to check which choices you
have. Normally you should use ‘iso8859’ for registry and
‘1’ for encoding.

The fourth and final method of specifying a font is to use a “font
nickname”. Certain fonts have shorter nicknames, which you can use
instead of a normal font specification. For instance, ‘6x13’ is
equivalent to

-misc-fixed-medium-r-semicondensed--13-*-*-*-c-60-iso8859-1

On X, Emacs recognizes two types of fonts: client-side fonts,
which are provided by the Xft and Fontconfig libraries, and
server-side fonts, which are provided by the X server itself.
Most client-side fonts support advanced font features such as
antialiasing and subpixel hinting, while server-side fonts do not.
Fontconfig and GTK patterns match only client-side fonts.

You will probably want to use a fixed-width default font—that is,
a font in which all characters have the same width. For Xft and
Fontconfig fonts, you can use the fc-list command to list
the available fixed-width fonts, like this:

fc-list :spacing=mono fc-list :spacing=charcell

For server-side X fonts, you can use the xlsfonts program to
list the available fixed-width fonts, like this:

21.9 Speedbar Frames

The speedbar is a special frame for conveniently navigating in
or operating on another frame. The speedbar, when it exists, is
always associated with a specific frame, called its attached
frame; all speedbar operations act on that frame.

Type M-x speedbar to create the speedbar and associate it with
the current frame. To dismiss the speedbar, type M-x speedbar
again, or select the speedbar and type q. (You can also delete
the speedbar frame like any other Emacs frame.) If you wish to
associate the speedbar with a different frame, dismiss it and call
M-x speedbar from that frame.

The speedbar can operate in various modes. Its default mode is
File Display mode, which shows the files in the current
directory of the selected window of the attached frame, one file per
line. Clicking on a file name visits that file in the selected window
of the attached frame, and clicking on a directory name shows that
directory in the speedbar (see Mouse References). Each line also
has a box, ‘[+]’ or ‘<+>’, that you can click on to
expand the contents of that item. Expanding a directory adds
the contents of that directory to the speedbar display, underneath the
directory’s own line. Expanding an ordinary file adds a list of the
tags in that file to the speedbar display; you can click on a tag name
to jump to that tag in the selected window of the attached frame.
When a file or directory is expanded, the ‘[+]’ changes to
‘[-]’; you can click on that box to contract the item,
hiding its contents.

You navigate through the speedbar using the keyboard, too. Typing
RET while point is on a line in the speedbar is equivalent to
clicking the item on the current line, and SPC expands or
contracts the item. U displays the parent directory of the
current directory. To copy, delete, or rename the file on the current
line, type C, D, and R respectively. To create a
new directory, type M.

Another general-purpose speedbar mode is Buffer Display mode;
in this mode, the speedbar displays a list of Emacs buffers. To
switch to this mode, type b in the speedbar. To return to File
Display mode, type f. You can also change the display mode by
clicking mouse-3 anywhere in the speedbar window (or
mouse-1 on the mode-line) and selecting ‘Displays’ in the
pop-up menu.

Some major modes, including Rmail mode, Info, and GUD, have
specialized ways of putting useful items into the speedbar for you to
select. For example, in Rmail mode, the speedbar shows a list of Rmail
files, and lets you move the current message to another Rmail file by
clicking on its ‘<M>’ box.

For more details on using and programming the speedbar, See Speedbar in Speedbar Manual.

21.10 Multiple Displays

A single Emacs can talk to more than one X display. Initially, Emacs
uses just one display—the one specified with the DISPLAY
environment variable or with the ‘--display’ option (see Initial Options). To connect to another display, use the command
make-frame-on-display:

M-x make-frame-on-display RETdisplayRET

Create a new frame on display display.

A single X server can handle more than one screen. When you open
frames on two screens belonging to one server, Emacs knows they share a
single keyboard, and it treats all the commands arriving from these
screens as a single stream of input.

When you open frames on different X servers, Emacs makes a separate
input stream for each server. Each server also has its own selected
frame. The commands you enter with a particular X server apply to
that server’s selected frame.

21.11 Frame Parameters

You can control the default appearance and behavior of all frames by
specifying a default list of frame parameters in the variable
default-frame-alist. Its value should be a list of entries,
each specifying a parameter name and a value for that parameter.
These entries take effect whenever Emacs creates a new frame,
including the initial frame.

For example, you can add the following lines to your init file
(see Init File) to set the default frame width to 90 character
columns, the default frame height to 40 character rows, and the
default font to ‘Monospace-10’:

21.12 Scroll Bars

On graphical displays, there is a scroll bar on the side of
each Emacs window. Clicking Mouse-1 on the scroll bar’s up and
down buttons scrolls the window by one line at a time. Clicking
Mouse-1 above or below the scroll bar’s inner box scrolls the
window by nearly the entire height of the window, like M-v and
C-v respectively (see Moving Point). Dragging the inner box
scrolls continuously.

If Emacs is compiled on the X Window System without X toolkit
support, the scroll bar behaves differently. Clicking Mouse-1
anywhere on the scroll bar scrolls forward like C-v, while
Mouse-3 scrolls backward like M-v. Clicking Mouse-2
in the scroll bar lets you drag the inner box up and down.

To toggle the use of scroll bars, type M-x scroll-bar-mode.
This command applies to all frames, including frames yet to be
created. To toggle scroll bars for just the selected frame, use the
command M-x toggle-scroll-bar.

To control the use of scroll bars at startup, customize the variable
scroll-bar-mode. Its value should be either right (put
scroll bars on the right side of windows), left (put them on
the left), or nil (disable scroll bars). By default, Emacs
puts scroll bars on the right if it was compiled with GTK+ support on
the X Window System, and on MS-Windows or Mac OS; Emacs puts scroll
bars on the left if compiled on the X Window System without GTK+
support (following the old convention for X applications).

You can also use the X resource ‘verticalScrollBars’ to enable
or disable the scroll bars (see Resources). To control the scroll
bar width, change the scroll-bar-width frame parameter
(see Frame Parameters in The Emacs Lisp Reference Manual).

If you’re using Emacs on X (with GTK+ or Motif), you can customize the
variable scroll-bar-adjust-thumb-portion to control
overscrolling of the scroll bar, i.e. dragging the thumb down even
when the end of the buffer is visible. If its value is
non-nil, the scroll bar can be dragged downwards even if the
end of the buffer is shown; if nil, the thumb will be at the
bottom when the end of the buffer is shown. You can not over-scroll
when the entire buffer is visible.

The visual appearance of the scroll bars is controlled by the
scroll-bar face.

21.13 Drag and Drop

In most graphical desktop environments, Emacs has basic support for
drag and drop operations. For instance, dropping text onto an
Emacs frame inserts the text where it is dropped. Dropping a file
onto an Emacs frame visits that file. As a special case, dropping the
file on a Dired buffer moves or copies the file (according to the
conventions of the application it came from) into the directory
displayed in that buffer.

Dropping a file normally visits it in the window you drop it on. If
you prefer to visit the file in a new window in such cases, customize
the variable dnd-open-file-other-window.

The XDND and Motif drag and drop protocols, and the old KDE 1.x
protocol, are currently supported.

21.14 Menu Bars

You can toggle the use of menu bars with M-x menu-bar-mode.
With no argument, this command toggles Menu Bar mode, a global minor
mode. With an argument, the command turns Menu Bar mode on if the
argument is positive, off if the argument is not positive. To control
the use of menu bars at startup, customize the variable
menu-bar-mode.

Expert users often turn off the menu bar, especially on text
terminals, where this makes one additional line available for text.
If the menu bar is off, you can still pop up a menu of its contents
with C-Mouse-3 on a display which supports pop-up menus.
See Menu Mouse Clicks.

See Menu Bar, for information on how to invoke commands with the
menu bar. See X Resources, for how to customize the menu bar
menus’ visual appearance.

21.15 Tool Bars

On graphical displays, Emacs puts a tool bar at the top of
each frame, just below the menu bar. This is a row of icons which you
can click on with the mouse to invoke various commands.

The global (default) tool bar contains general commands. Some major
modes define their own tool bars; whenever a buffer with such a major
mode is current, the mode’s tool bar replaces the global tool bar.

To toggle the use of tool bars, type M-x tool-bar-mode. This
command applies to all frames, including frames yet to be created. To
control the use of tool bars at startup, customize the variable
tool-bar-mode.

When Emacs is compiled with GTK+ support, each tool bar item can
consist of an image, or a text label, or both. By default, Emacs
follows the Gnome desktop’s tool bar style setting; if none is
defined, it displays tool bar items as just images. To impose a
specific tool bar style, customize the variable tool-bar-style.

You can also control the placement of the tool bar for the GTK+ tool
bar with the frame parameter tool-bar-position. See Frame
Parameters in The Emacs Lisp Reference Manual.

21.16 Using Dialog Boxes

A dialog box is a special kind of menu for asking you a yes-or-no
question or some other special question. Many Emacs commands use a
dialog box to ask a yes-or-no question, if you used the mouse to
invoke the command that led to the question.

To disable the use of dialog boxes, change the variable
use-dialog-box to nil. In that case, Emacs always
performs yes-or-no prompts using the echo area and keyboard input.
This variable also controls whether to use file selection windows (but
those are not supported on all platforms).

A file selection window is a special kind of dialog box for asking
for file names. You can customize the variable use-file-dialog
to suppress the use of file selection windows, even if you still want
other kinds of dialogs. This variable has no effect if you have
suppressed all dialog boxes with the variable use-dialog-box.

When Emacs is compiled with GTK+ support, it uses the GTK+ “file
chooser” dialog. Emacs adds an additional toggle button to this
dialog, which you can use to enable or disable the display of hidden
files (files starting with a dot) in that dialog. If you want this
toggle to be activated by default, change the variable
x-gtk-show-hidden-files to t. In addition, Emacs adds
help text to the GTK+ file chooser dialog; to disable this help text,
change the variable x-gtk-file-dialog-help-text to nil.

21.17 Tooltips

Tooltips are small windows that display text information at
the current mouse position. They activate when there is a pause in
mouse movement over some significant piece of text in a window, or the
mode line, or some other part of the Emacs frame such as a tool bar
button or menu item.

You can toggle the use of tooltips with the command M-x
tooltip-mode. When Tooltip mode is disabled, the help text is
displayed in the echo area instead. To control the use of tooltips at
startup, customize the variable tooltip-mode.

The variables tooltip-delay specifies how long Emacs should
wait before displaying a tooltip. For additional customization
options for displaying tooltips, use M-x customize-group
RET tooltip RET.

If Emacs is built with GTK+ support, it displays tooltips via GTK+,
using the default appearance of GTK+ tooltips. To disable this,
change the variable x-gtk-use-system-tooltips to nil.
If you do this, or if Emacs is built without GTK+ support, most
attributes of the tooltip text are specified by the tooltip
face, and by X resources (see X Resources).

GUD tooltips are special tooltips that show the values of
variables when debugging a program with GUD. See Debugger Operation.

21.18 Mouse Avoidance

On graphical terminals, the mouse pointer may obscure the text in
the Emacs frame. Emacs provides two methods to avoid this problem.

Firstly, Emacs hides the mouse pointer each time you type a
self-inserting character, if the pointer lies inside an Emacs frame;
moving the mouse pointer makes it visible again. To disable this
feature, set the variable make-pointer-invisible to nil.

Secondly, you can use Mouse Avoidance mode, a minor mode, to keep
the mouse pointer away from point. To use Mouse Avoidance mode,
customize the variable mouse-avoidance-mode. You can set this
to various values to move the mouse in several ways:

banish

Move the pointer to a corner of the frame on any key-press. You can
customize the variable mouse-avoidance-banish-position to
specify where the pointer goes when it is banished.

exile

Banish the pointer only if the cursor gets too close, and allow it to
return once the cursor is out of the way.

jump

If the cursor gets too close to the pointer, displace the pointer by a
random distance and direction.

animate

As jump, but shows steps along the way for illusion of motion.

cat-and-mouse

The same as animate.

proteus

As animate, but changes the shape of the mouse pointer too.

You can also use the command M-x mouse-avoidance-mode to enable
the mode. Whenever Mouse Avoidance mode moves the mouse, it also
raises the frame.

21.19 Non-Window Terminals

On a text terminal, Emacs can display only one Emacs frame at a
time. However, you can still create multiple Emacs frames, and switch
between them. Switching frames on these terminals is much like
switching between different window configurations.

Use C-x 5 2 to create a new frame and switch to it; use C-x
5 o to cycle through the existing frames; use C-x 5 0 to delete
the current frame.

Each frame has a number to distinguish it. If your terminal can
display only one frame at a time, the selected frame’s number n
appears near the beginning of the mode line, in the form
‘Fn’.

‘Fn’ is in fact the frame’s initial name. You can give
frames more meaningful names if you wish, and you can select a frame
by its name. Use the command M-x set-frame-name RETnameRET to specify a new name for the selected frame,
and use M-x select-frame-by-name RETnameRET
to select a frame according to its name. The name you specify appears
in the mode line when the frame is selected.

21.20 Using a Mouse in Text Terminals

Some text terminals support mouse clicks in the terminal window.

In a terminal emulator which is compatible with xterm, you
can use M-x xterm-mouse-mode to give Emacs control over simple
uses of the mouse—basically, only non-modified single clicks are
supported. The normal xterm mouse functionality for such
clicks is still available by holding down the SHIFT key when you
press the mouse button. Xterm Mouse mode is a global minor mode
(see Minor Modes). Repeating the command turns the mode off
again.

In the console on GNU/Linux, you can use M-x gpm-mouse-mode to
enable mouse support. You must have the gpm server installed and
running on your system in order for this to work.

22 International Character Set Support

Emacs supports a wide variety of international character sets,
including European and Vietnamese variants of the Latin alphabet, as
well as Arabic scripts, Brahmic scripts (for languages such as
Bengali, Hindi, and Thai), Cyrillic, Ethiopic, Georgian, Greek, Han
(for Chinese and Japanese), Hangul (for Korean), Hebrew and IPA.
Emacs also supports various encodings of these characters that are used by
other internationalized software, such as word processors and mailers.

Emacs allows editing text with international characters by supporting
all the related activities:

You can visit files with non-ASCII characters, save non-ASCII text, and
pass non-ASCII text between Emacs and programs it invokes (such as
compilers, spell-checkers, and mailers). Setting your language
environment (see Language Environments) takes care of setting up the
coding systems and other options for a specific language or culture.
Alternatively, you can specify how Emacs should encode or decode text
for each command; see Text Coding.

You can display non-ASCII characters encoded by the various
scripts. This works by using appropriate fonts on graphics displays
(see Defining Fontsets), and by sending special codes to text
displays (see Terminal Coding). If some characters are displayed
incorrectly, refer to Undisplayable Characters, which describes
possible problems and explains how to solve them.

Characters from scripts whose natural ordering of text is from right
to left are reordered for display (see Bidirectional Editing).
These scripts include Arabic, Hebrew, Syriac, Thaana, and a few
others.

You can insert non-ASCII characters or search for them. To do that,
you can specify an input method (see Select Input Method) suitable
for your language, or use the default input method set up when you chose
your language environment. If
your keyboard can produce non-ASCII characters, you can select an
appropriate keyboard coding system (see Terminal Coding), and Emacs
will accept those characters. Latin-1 characters can also be input by
using the C-x 8 prefix, see Unibyte Mode.

With the X Window System, your locale should be set to an appropriate
value to make sure Emacs interprets keyboard input correctly; see
locales.

22.1 Introduction to International Character Sets

The users of international character sets and scripts have
established many more-or-less standard coding systems for storing
files. These coding systems are typically multibyte, meaning
that sequences of two or more bytes are used to represent individual
non-ASCII characters.

Internally, Emacs uses its own multibyte character encoding, which
is a superset of the Unicode standard. This internal encoding
allows characters from almost every known script to be intermixed in a
single buffer or string. Emacs translates between the multibyte
character encoding and various other coding systems when reading and
writing files, and when exchanging data with subprocesses.

The command C-h h (view-hello-file) displays the file
etc/HELLO, which illustrates various scripts by showing
how to say “hello” in many languages. If some characters can’t be
displayed on your terminal, they appear as ‘?’ or as hollow boxes
(see Undisplayable Characters).

Keyboards, even in the countries where these character sets are
used, generally don’t have keys for all the characters in them. You
can insert characters that your keyboard does not support, using
C-q (quoted-insert) or C-x 8 RET
(insert-char). See Inserting Text. Emacs also supports
various input methods, typically one for each script or
language, which make it easier to type characters in the script.
See Input Methods.

The prefix key C-x RET is used for commands that pertain
to multibyte characters, coding systems, and input methods.

The command C-x = (what-cursor-position) shows
information about the character at point. In addition to the
character position, which was described in Position Info, this
command displays how the character is encoded. For instance, it
displays the following line in the echo area for the character
‘c’:

Char: c (99, #o143, #x63) point=28062 of 36168 (78%) column=53

The four values after ‘Char:’ describe the character that
follows point, first by showing it and then by giving its character
code in decimal, octal and hex. For a non-ASCII multibyte
character, these are followed by ‘file’ and the character’s
representation, in hex, in the buffer’s coding system, if that coding
system encodes the character safely and with a single byte
(see Coding Systems). If the character’s encoding is longer than
one byte, Emacs shows ‘file ...’.

As a special case, if the character lies in the range 128 (0200
octal) through 159 (0237 octal), it stands for a “raw” byte that
does not correspond to any specific displayable character. Such a
“character” lies within the eight-bit-control character set,
and is displayed as an escaped octal character code. In this case,
C-x = shows ‘part of display ...’ instead of ‘file’.

With a prefix argument (C-u C-x =), this command displays a
detailed description of the character in a window:

The character set name, and the codes that identify the character
within that character set; ASCII characters are identified
as belonging to the ascii character set.

The character’s script, syntax and categories.

What keys to type to input the character in the current input method
(if it supports the character).

The character’s encodings, both internally in the buffer, and externally
if you were to save the file.

If you are running Emacs on a graphical display, the font name and
glyph code for the character. If you are running Emacs on a text
terminal, the code(s) sent to the terminal.

The character’s text properties (see Text Properties in the Emacs Lisp Reference Manual), including any non-default
faces used to display the character, and any overlays containing it
(see Overlays in the same manual).

22.2 Language Environments

All supported character sets are supported in Emacs buffers whenever
multibyte characters are enabled; there is no need to select a
particular language in order to display its characters.
However, it is important to select a language
environment in order to set various defaults. Roughly speaking, the
language environment represents a choice of preferred script rather
than a choice of language.

The language environment controls which coding systems to recognize
when reading text (see Recognize Coding). This applies to files,
incoming mail, and any other text you read into Emacs. It may also
specify the default coding system to use when you create a file. Each
language environment also specifies a default input method.

To select a language environment, customize
current-language-environment or use the command M-x
set-language-environment. It makes no difference which buffer is
current when you use this command, because the effects apply globally
to the Emacs session. See the variable language-info-alist for
the list of supported language environments, and use the command
C-h L lang-envRET (describe-language-environment)
for more information about the language environment lang-env.
Supported language environments include:

To display the script(s) used by your language environment on a
graphical display, you need to have suitable fonts.
See Fontsets, for more details about setting up your fonts.

Some operating systems let you specify the character-set locale you
are using by setting the locale environment variables LC_ALL,
LC_CTYPE, or LANG. (If more than one of these is
set, the first one that is nonempty specifies your locale for this
purpose.) During startup, Emacs looks up your character-set locale’s
name in the system locale alias table, matches its canonical name
against entries in the value of the variables
locale-charset-language-names and locale-language-names
(the former overrides the latter),
and selects the corresponding language environment if a match is found.
It also adjusts the display
table and terminal coding system, the locale coding system, the
preferred coding system as needed for the locale, and—last but not
least—the way Emacs decodes non-ASCII characters sent by your keyboard.

If you modify the LC_ALL, LC_CTYPE, or LANG
environment variables while running Emacs (by using M-x setenv),
you may want to invoke the set-locale-environment
function afterwards to readjust the language environment from the new
locale.

The set-locale-environment function normally uses the preferred
coding system established by the language environment to decode system
messages. But if your locale matches an entry in the variable
locale-preferred-coding-systems, Emacs uses the corresponding
coding system instead. For example, if the locale ‘ja_JP.PCK’
matches japanese-shift-jis in
locale-preferred-coding-systems, Emacs uses that encoding even
though it might normally use japanese-iso-8bit.

You can override the language environment chosen at startup with
explicit use of the command set-language-environment, or with
customization of current-language-environment in your init
file.

To display information about the effects of a certain language
environment lang-env, use the command C-h L lang-envRET (describe-language-environment). This tells you
which languages this language environment is useful for, and lists the
character sets, coding systems, and input methods that go with it. It
also shows some sample text to illustrate scripts used in this
language environment. If you give an empty input for lang-env,
this command describes the chosen language environment.

You can customize any language environment with the normal hook
set-language-environment-hook. The command
set-language-environment runs that hook after setting up the new
language environment. The hook functions can test for a specific
language environment by checking the variable
current-language-environment. This hook is where you should
put non-default settings for specific language environments, such as
coding systems for keyboard input and terminal output, the default
input method, etc.

Before it starts to set up the new language environment,
set-language-environment first runs the hook
exit-language-environment-hook. This hook is useful for undoing
customizations that were made with set-language-environment-hook.
For instance, if you set up a special key binding in a specific language
environment using set-language-environment-hook, you should set
up exit-language-environment-hook to restore the normal binding
for that key.

22.3 Input Methods

An input method is a kind of character conversion designed
specifically for interactive input. In Emacs, typically each language
has its own input method; sometimes several languages that use the same
characters can share one input method. A few languages support several
input methods.

The simplest kind of input method works by mapping ASCII letters
into another alphabet; this allows you to use one other alphabet
instead of ASCII. The Greek and Russian input methods
work this way.

A more powerful technique is composition: converting sequences of
characters into one letter. Many European input methods use composition
to produce a single non-ASCII letter from a sequence that consists of a
letter followed by accent characters (or vice versa). For example, some
methods convert the sequence o ^ into a single accented letter.
These input methods have no special commands of their own; all they do
is compose sequences of printing characters.

The input methods for syllabic scripts typically use mapping followed
by composition. The input methods for Thai and Korean work this way.
First, letters are mapped into symbols for particular sounds or tone
marks; then, sequences of these that make up a whole syllable are
mapped into one syllable sign.

Chinese and Japanese require more complex methods. In Chinese input
methods, first you enter the phonetic spelling of a Chinese word (in
input method chinese-py, among others), or a sequence of
portions of the character (input methods chinese-4corner and
chinese-sw, and others). One input sequence typically
corresponds to many possible Chinese characters. You select the one
you mean using keys such as C-f, C-b, C-n,
C-p (or the arrow keys), and digits, which have special meanings
in this situation.

The possible characters are conceptually arranged in several rows,
with each row holding up to 10 alternatives. Normally, Emacs displays
just one row at a time, in the echo area; (i/j)
appears at the beginning, to indicate that this is the ith row
out of a total of j rows. Type C-n or C-p to
display the next row or the previous row.

Type C-f and C-b to move forward and backward among
the alternatives in the current row. As you do this, Emacs highlights
the current alternative with a special color; type C-SPC
to select the current alternative and use it as input. The
alternatives in the row are also numbered; the number appears before
the alternative. Typing a number selects the associated alternative
of the current row and uses it as input.

TAB in these Chinese input methods displays a buffer showing
all the possible characters at once; then clicking Mouse-2 on
one of them selects that alternative. The keys C-f, C-b,
C-n, C-p, and digits continue to work as usual, but they
do the highlighting in the buffer showing the possible characters,
rather than in the echo area.

In Japanese input methods, first you input a whole word using
phonetic spelling; then, after the word is in the buffer, Emacs
converts it into one or more characters using a large dictionary. One
phonetic spelling corresponds to a number of different Japanese words;
to select one of them, use C-n and C-p to cycle through
the alternatives.

Sometimes it is useful to cut off input method processing so that the
characters you have just entered will not combine with subsequent
characters. For example, in input method latin-1-postfix, the
sequence o ^ combines to form an ‘o’ with an accent. What if
you want to enter them as separate characters?

One way is to type the accent twice; this is a special feature for
entering the separate letter and accent. For example, o ^ ^ gives
you the two characters ‘o^’. Another way is to type another letter
after the o—something that won’t combine with that—and
immediately delete it. For example, you could type o o DEL
^ to get separate ‘o’ and ‘^’.

Another method, more general but not quite as easy to type, is to use
C-\ C-\ between two characters to stop them from combining. This
is the command C-\ (toggle-input-method) used twice.
See Select Input Method.

C-\ C-\ is especially useful inside an incremental search,
because it stops waiting for more characters to combine, and starts
searching for what you have already entered.

To find out how to input the character after point using the current
input method, type C-u C-x =. See Position Info.

The variables input-method-highlight-flag and
input-method-verbose-flag control how input methods explain
what is happening. If input-method-highlight-flag is
non-nil, the partial sequence is highlighted in the buffer (for
most input methods—some disable this feature). If
input-method-verbose-flag is non-nil, the list of
possible characters to type next is displayed in the echo area (but
not when you are in the minibuffer).

Another facility for typing characters not on your keyboard is by
using C-x 8 RET (insert-char) to insert a single
character based on its Unicode name or code-point; see Inserting Text.

22.4 Selecting an Input Method

C-\

Enable or disable use of the selected input method (toggle-input-method).

C-x RET C-\ methodRET

Select a new input method for the current buffer (set-input-method).

C-h I methodRET

C-h C-\ methodRET

Describe the input method method (describe-input-method).
By default, it describes the current input method (if any). This
description should give you the full details of how to use any
particular input method.

M-x list-input-methods

Display a list of all the supported input methods.

To choose an input method for the current buffer, use C-x
RET C-\ (set-input-method). This command reads the
input method name from the minibuffer; the name normally starts with the
language environment that it is meant to be used with. The variable
current-input-method records which input method is selected.

Input methods use various sequences of ASCII characters to
stand for non-ASCII characters. Sometimes it is useful to
turn off the input method temporarily. To do this, type C-\
(toggle-input-method). To reenable the input method, type
C-\ again.

If you type C-\ and you have not yet selected an input method,
it prompts you to specify one. This has the same effect as using
C-x RET C-\ to specify an input method.

When invoked with a numeric argument, as in C-u C-\,
toggle-input-method always prompts you for an input method,
suggesting the most recently selected one as the default.

Selecting a language environment specifies a default input method for
use in various buffers. When you have a default input method, you can
select it in the current buffer by typing C-\. The variable
default-input-method specifies the default input method
(nil means there is none).

In some language environments, which support several different input
methods, you might want to use an input method different from the
default chosen by set-language-environment. You can instruct
Emacs to select a different default input method for a certain
language environment, if you wish, by using
set-language-environment-hook (see set-language-environment-hook). For example:

This automatically activates the input method “german-prefix” in
Text mode.

Some input methods for alphabetic scripts work by (in effect)
remapping the keyboard to emulate various keyboard layouts commonly used
for those scripts. How to do this remapping properly depends on your
actual keyboard layout. To specify which layout your keyboard has, use
the command M-x quail-set-keyboard-layout.

You can use the command M-x quail-show-key to show what key (or
key sequence) to type in order to input the character following point,
using the selected keyboard layout. The command C-u C-x = also
shows that information, in addition to other information about the
character.

M-x list-input-methods displays a list of all the supported
input methods. The list gives information about each input method,
including the string that stands for it in the mode line.

22.5 Coding Systems

Users of various languages have established many more-or-less standard
coding systems for representing them. Emacs does not use these coding
systems internally; instead, it converts from various coding systems to
its own system when reading data, and converts the internal coding
system to other coding systems when writing data. Conversion is
possible in reading or writing files, in sending or receiving from the
terminal, and in exchanging data with subprocesses.

Emacs assigns a name to each coding system. Most coding systems are
used for one language, and the name of the coding system starts with
the language name. Some coding systems are used for several
languages; their names usually start with ‘iso’. There are also
special coding systems, such as no-conversion, raw-text,
and emacs-internal.

A special class of coding systems, collectively known as
codepages, is designed to support text encoded by MS-Windows and
MS-DOS software. The names of these coding systems are
cpnnnn, where nnnn is a 3- or 4-digit number of the
codepage. You can use these encodings just like any other coding
system; for example, to visit a file encoded in codepage 850, type
C-x RET c cp850 RET C-x C-f filenameRET.

In addition to converting various representations of non-ASCII
characters, a coding system can perform end-of-line conversion. Emacs
handles three different conventions for how to separate lines in a file:
newline (“unix”), carriage-return linefeed (“dos”), and just
carriage-return (“mac”).

C-h C codingRET

Describe coding system coding (describe-coding-system).

C-h C RET

Describe the coding systems currently in use.

M-x list-coding-systems

Display a list of all the supported coding systems.

The command C-h C (describe-coding-system) displays
information about particular coding systems, including the end-of-line
conversion specified by those coding systems. You can specify a coding
system name as the argument; alternatively, with an empty argument, it
describes the coding systems currently selected for various purposes,
both in the current buffer and as the defaults, and the priority list
for recognizing coding systems (see Recognize Coding).

To display a list of all the supported coding systems, type M-x
list-coding-systems. The list gives information about each coding
system, including the letter that stands for it in the mode line
(see Mode Line).

Each of the coding systems that appear in this list—except for
no-conversion, which means no conversion of any kind—specifies
how and whether to convert printing characters, but leaves the choice of
end-of-line conversion to be decided based on the contents of each file.
For example, if the file appears to use the sequence carriage-return
linefeed to separate lines, DOS end-of-line conversion will be used.

Each of the listed coding systems has three variants, which specify
exactly what to do for end-of-line conversion:

…-unix

Don’t do any end-of-line conversion; assume the file uses
newline to separate lines. (This is the convention normally used
on Unix and GNU systems, and Mac OS X.)

…-dos

Assume the file uses carriage-return linefeed to separate lines, and do
the appropriate conversion. (This is the convention normally used on
Microsoft systems.8)

…-mac

Assume the file uses carriage-return to separate lines, and do the
appropriate conversion. (This was the convention used on the
Macintosh system prior to OS X.)

These variant coding systems are omitted from the
list-coding-systems display for brevity, since they are entirely
predictable. For example, the coding system iso-latin-1 has
variants iso-latin-1-unix, iso-latin-1-dos and
iso-latin-1-mac.

The coding systems unix, dos, and mac are
aliases for undecided-unix, undecided-dos, and
undecided-mac, respectively. These coding systems specify only
the end-of-line conversion, and leave the character code conversion to
be deduced from the text itself.

The coding system raw-text is good for a file which is mainly
ASCII text, but may contain byte values above 127 that are
not meant to encode non-ASCII characters. With
raw-text, Emacs copies those byte values unchanged, and sets
enable-multibyte-characters to nil in the current buffer
so that they will be interpreted properly. raw-text handles
end-of-line conversion in the usual way, based on the data
encountered, and has the usual three variants to specify the kind of
end-of-line conversion to use.

In contrast, the coding system no-conversion specifies no
character code conversion at all—none for non-ASCII byte values and
none for end of line. This is useful for reading or writing binary
files, tar files, and other files that must be examined verbatim. It,
too, sets enable-multibyte-characters to nil.

The easiest way to edit a file with no conversion of any kind is with
the M-x find-file-literally command. This uses
no-conversion, and also suppresses other Emacs features that
might convert the file contents before you see them. See Visiting.

The coding system emacs-internal (or utf-8-emacs,
which is equivalent) means that the file contains non-ASCII
characters stored with the internal Emacs encoding. This coding
system handles end-of-line conversion based on the data encountered,
and has the usual three variants to specify the kind of end-of-line
conversion.

22.6 Recognizing Coding Systems

Whenever Emacs reads a given piece of text, it tries to recognize
which coding system to use. This applies to files being read, output
from subprocesses, text from X selections, etc. Emacs can select the
right coding system automatically most of the time—once you have
specified your preferences.

Some coding systems can be recognized or distinguished by which byte
sequences appear in the data. However, there are coding systems that
cannot be distinguished, not even potentially. For example, there is no
way to distinguish between Latin-1 and Latin-2; they use the same byte
values with different meanings.

Emacs handles this situation by means of a priority list of coding
systems. Whenever Emacs reads a file, if you do not specify the coding
system to use, Emacs checks the data against each coding system,
starting with the first in priority and working down the list, until it
finds a coding system that fits the data. Then it converts the file
contents assuming that they are represented in this coding system.

The priority list of coding systems depends on the selected language
environment (see Language Environments). For example, if you use
French, you probably want Emacs to prefer Latin-1 to Latin-2; if you use
Czech, you probably want Latin-2 to be preferred. This is one of the
reasons to specify a language environment.

However, you can alter the coding system priority list in detail
with the command M-x prefer-coding-system. This command reads
the name of a coding system from the minibuffer, and adds it to the
front of the priority list, so that it is preferred to all others. If
you use this command several times, each use adds one element to the
front of the priority list.

If you use a coding system that specifies the end-of-line conversion
type, such as iso-8859-1-dos, what this means is that Emacs
should attempt to recognize iso-8859-1 with priority, and should
use DOS end-of-line conversion when it does recognize iso-8859-1.

Sometimes a file name indicates which coding system to use for the
file. The variable file-coding-system-alist specifies this
correspondence. There is a special function
modify-coding-system-alist for adding elements to this list. For
example, to read and write all ‘.txt’ files using the coding system
chinese-iso-8bit, you can execute this Lisp expression:

(modify-coding-system-alist 'file "\\.txt\\'" 'chinese-iso-8bit)

The first argument should be file, the second argument should be
a regular expression that determines which files this applies to, and
the third argument says which coding system to use for these files.

Emacs recognizes which kind of end-of-line conversion to use based on
the contents of the file: if it sees only carriage-returns, or only
carriage-return linefeed sequences, then it chooses the end-of-line
conversion accordingly. You can inhibit the automatic use of
end-of-line conversion by setting the variable inhibit-eol-conversion
to non-nil. If you do that, DOS-style files will be displayed
with the ‘^M’ characters visible in the buffer; some people
prefer this to the more subtle ‘(DOS)’ end-of-line type
indication near the left edge of the mode line (see eol-mnemonic).

By default, the automatic detection of coding system is sensitive to
escape sequences. If Emacs sees a sequence of characters that begin
with an escape character, and the sequence is valid as an ISO-2022
code, that tells Emacs to use one of the ISO-2022 encodings to decode
the file.

However, there may be cases that you want to read escape sequences
in a file as is. In such a case, you can set the variable
inhibit-iso-escape-detection to non-nil. Then the code
detection ignores any escape sequences, and never uses an ISO-2022
encoding. The result is that all escape sequences become visible in
the buffer.

The default value of inhibit-iso-escape-detection is
nil. We recommend that you not change it permanently, only for
one specific operation. That’s because some Emacs Lisp source files
in the Emacs distribution contain non-ASCII characters encoded in the
coding system iso-2022-7bit, and they won’t be
decoded correctly when you visit those files if you suppress the
escape sequence detection.

The variables auto-coding-alist and
auto-coding-regexp-alist are
the strongest way to specify the coding system for certain patterns of
file names, or for files containing certain patterns, respectively.
These variables even override ‘-*-coding:-*-’ tags in the file
itself (see Specify Coding). For example, Emacs
uses auto-coding-alist for tar and archive files, to prevent it
from being confused by a ‘-*-coding:-*-’ tag in a member of the
archive and thinking it applies to the archive file as a whole.

Another way to specify a coding system is with the variable
auto-coding-functions. For example, one of the builtin
auto-coding-functions detects the encoding for XML files.
Unlike the previous two, this variable does not override any
‘-*-coding:-*-’ tag.

22.7 Specifying a File’s Coding System

If Emacs recognizes the encoding of a file incorrectly, you can
reread the file using the correct coding system with C-x
RET r (revert-buffer-with-coding-system). This command
prompts for the coding system to use. To see what coding system Emacs
actually used to decode the file, look at the coding system mnemonic
letter near the left edge of the mode line (see Mode Line), or
type C-h C (describe-coding-system).

You can specify the coding system for a particular file in the file
itself, using the ‘-*-…-*-’ construct at the beginning,
or a local variables list at the end (see File Variables). You do
this by defining a value for the “variable” named coding.
Emacs does not really have a variable coding; instead of
setting a variable, this uses the specified coding system for the
file. For example, ‘-*-mode: C; coding: latin-1;-*-’ specifies
use of the Latin-1 coding system, as well as C mode. When you specify
the coding explicitly in the file, that overrides
file-coding-system-alist.

22.8 Choosing Coding Systems for Output

Once Emacs has chosen a coding system for a buffer, it stores that
coding system in buffer-file-coding-system. That makes it the
default for operations that write from this buffer into a file, such
as save-buffer and write-region. You can specify a
different coding system for further file output from the buffer using
set-buffer-file-coding-system (see Text Coding).

You can insert any character Emacs supports into any Emacs buffer,
but most coding systems can only handle a subset of these characters.
Therefore, it’s possible that the characters you insert cannot be
encoded with the coding system that will be used to save the buffer.
For example, you could visit a text file in Polish, encoded in
iso-8859-2, and add some Russian words to it. When you save
that buffer, Emacs cannot use the current value of
buffer-file-coding-system, because the characters you added
cannot be encoded by that coding system.

When that happens, Emacs tries the most-preferred coding system (set
by M-x prefer-coding-system or M-x
set-language-environment). If that coding system can safely encode
all of the characters in the buffer, Emacs uses it, and stores its
value in buffer-file-coding-system. Otherwise, Emacs displays
a list of coding systems suitable for encoding the buffer’s contents,
and asks you to choose one of those coding systems.

If you insert the unsuitable characters in a mail message, Emacs
behaves a bit differently. It additionally checks whether the
most-preferred coding system is recommended for use in MIME messages;
if not, it informs you of this fact and prompts you for another coding
system. This is so you won’t inadvertently send a message encoded in
a way that your recipient’s mail software will have difficulty
decoding. (You can still use an unsuitable coding system if you enter
its name at the prompt.)

When you send a mail message (see Sending Mail),
Emacs has four different ways to determine the coding system to use
for encoding the message text. It tries the buffer’s own value of
buffer-file-coding-system, if that is non-nil.
Otherwise, it uses the value of sendmail-coding-system, if that
is non-nil. The third way is to use the default coding system
for new files, which is controlled by your choice of language
environment, if that is non-nil. If all of these three values
are nil, Emacs encodes outgoing mail using the Latin-1 coding
system.

22.9 Specifying a Coding System for File Text

In cases where Emacs does not automatically choose the right coding
system for a file’s contents, you can use these commands to specify
one:

C-x RET f codingRET

Use coding system coding to save or revisit the file in
the current buffer (set-buffer-file-coding-system).

C-x RET c codingRET

Specify coding system coding for the immediately following
command (universal-coding-system-argument).

C-x RET r codingRET

Revisit the current file using the coding system coding
(revert-buffer-with-coding-system).

M-x recode-region RETrightRETwrongRET

Convert a region that was decoded using coding system wrong,
decoding it using coding system right instead.

The command C-x RET f
(set-buffer-file-coding-system) sets the file coding system for
the current buffer (i.e., the coding system to use when saving or
reverting the file). You specify which coding system using the
minibuffer. You can also invoke this command by clicking with
Mouse-3 on the coding system indicator in the mode line
(see Mode Line).

If you specify a coding system that cannot handle all the characters
in the buffer, Emacs will warn you about the troublesome characters,
and ask you to choose another coding system, when you try to save the
buffer (see Output Coding).

You can also use this command to specify the end-of-line conversion
(see end-of-line conversion) for encoding the
current buffer. For example, C-x RET f dos RET will
cause Emacs to save the current buffer’s text with DOS-style
carriage-return linefeed line endings.

Another way to specify the coding system for a file is when you visit
the file. First use the command C-x RET c
(universal-coding-system-argument); this command uses the
minibuffer to read a coding system name. After you exit the minibuffer,
the specified coding system is used for the immediately following
command.

So if the immediately following command is C-x C-f, for example,
it reads the file using that coding system (and records the coding
system for when you later save the file). Or if the immediately following
command is C-x C-w, it writes the file using that coding system.
When you specify the coding system for saving in this way, instead
of with C-x RET f, there is no warning if the buffer
contains characters that the coding system cannot handle.

Other file commands affected by a specified coding system include
C-x i and C-x C-v, as well as the other-window variants
of C-x C-f. C-x RET c also affects commands that
start subprocesses, including M-x shell (see Shell). If the
immediately following command does not use the coding system, then
C-x RET c ultimately has no effect.

An easy way to visit a file with no conversion is with the M-x
find-file-literally command. See Visiting.

The default value of the variable buffer-file-coding-system
specifies the choice of coding system to use when you create a new file.
It applies when you find a new file, and when you create a buffer and
then save it in a file. Selecting a language environment typically sets
this variable to a good choice of default coding system for that language
environment.

If you visit a file with a wrong coding system, you can correct this
with C-x RET r (revert-buffer-with-coding-system).
This visits the current file again, using a coding system you specify.

If a piece of text has already been inserted into a buffer using the
wrong coding system, you can redo the decoding of it using M-x
recode-region. This prompts you for the proper coding system, then
for the wrong coding system that was actually used, and does the
conversion. It first encodes the region using the wrong coding system,
then decodes it again using the proper coding system.

22.10 Coding Systems for Interprocess Communication

This section explains how to specify coding systems for use
in communication with other processes.

C-x RET x codingRET

Use coding system coding for transferring selections to and from
other graphical applications (set-selection-coding-system).

C-x RET X codingRET

Use coding system coding for transferring one
selection—the next one—to or from another graphical application
(set-next-selection-coding-system).

C-x RET p input-codingREToutput-codingRET

Use coding systems input-coding and output-coding for
subprocess input and output in the current buffer
(set-buffer-process-coding-system).

The command C-x RET x (set-selection-coding-system)
specifies the coding system for sending selected text to other windowing
applications, and for receiving the text of selections made in other
applications. This command applies to all subsequent selections, until
you override it by using the command again. The command C-x
RET X (set-next-selection-coding-system) specifies the
coding system for the next selection made in Emacs or read by Emacs.

The variable x-select-request-type specifies the data type to
request from the X Window System for receiving text selections from
other applications. If the value is nil (the default), Emacs
tries UTF8_STRING and COMPOUND_TEXT, in this order, and
uses various heuristics to choose the more appropriate of the two
results; if none of these succeed, Emacs falls back on STRING.
If the value of x-select-request-type is one of the symbols
COMPOUND_TEXT, UTF8_STRING, STRING, or
TEXT, Emacs uses only that request type. If the value is a
list of some of these symbols, Emacs tries only the request types in
the list, in order, until one of them succeeds, or until the list is
exhausted.

The command C-x RET p (set-buffer-process-coding-system)
specifies the coding system for input and output to a subprocess. This
command applies to the current buffer; normally, each subprocess has its
own buffer, and thus you can use this command to specify translation to
and from a particular subprocess by giving the command in the
corresponding buffer.

You can also use C-x RET c
(universal-coding-system-argument) just before the command that
runs or starts a subprocess, to specify the coding system for
communicating with that subprocess. See Text Coding.

The default for translation of process input and output depends on the
current language environment.

The variable locale-coding-system specifies a coding system
to use when encoding and decoding system strings such as system error
messages and format-time-string formats and time stamps. That
coding system is also used for decoding non-ASCII keyboard
input on the X Window System. You should choose a coding system that is compatible
with the underlying system’s text representation, which is normally
specified by one of the environment variables LC_ALL,
LC_CTYPE, and LANG. (The first one, in the order
specified above, whose value is nonempty is the one that determines
the text representation.)

22.11 Coding Systems for File Names

Use coding system coding for encoding and decoding file
names (set-file-name-coding-system).

The command C-x RET F (set-file-name-coding-system)
specifies a coding system to use for encoding file names. It
has no effect on reading and writing the contents of files.

In fact, all this command does is set the value of the variable
file-name-coding-system. If you set the variable to a coding
system name (as a Lisp symbol or a string), Emacs encodes file names
using that coding system for all file operations. This makes it
possible to use non-ASCII characters in file names—or, at
least, those non-ASCII characters that the specified coding
system can encode.

If file-name-coding-system is nil, Emacs uses a
default coding system determined by the selected language environment,
and stored in the default-file-name-coding-system variable.
In the default language environment, non-ASCII characters in
file names are not encoded specially; they appear in the file system
using the internal Emacs representation.

When Emacs runs on MS-Windows versions that are descendants of the
NT family (Windows 2000, XP, Vista, Windows 7, and Windows 8), the
value of file-name-coding-system is largely ignored, as Emacs
by default uses APIs that allow to pass Unicode file names directly.
By contrast, on Windows 9X, file names are encoded using
file-name-coding-system, which should be set to the codepage
(see codepage) pertinent for the current system
locale. The value of the variable w32-unicode-filenames
controls whether Emacs uses the Unicode APIs when it calls OS
functions that accept file names. This variable is set by the startup
code to nil on Windows 9X, and to t on newer versions of
MS-Windows.

Warning: if you change file-name-coding-system (or the
language environment) in the middle of an Emacs session, problems can
result if you have already visited files whose names were encoded using
the earlier coding system and cannot be encoded (or are encoded
differently) under the new coding system. If you try to save one of
these buffers under the visited file name, saving may use the wrong file
name, or it may encounter an error. If such a problem happens, use C-x
C-w to specify a new file name for that buffer.

If a mistake occurs when encoding a file name, use the command
M-x recode-file-name to change the file name’s coding
system. This prompts for an existing file name, its old coding
system, and the coding system to which you wish to convert.

22.12 Coding Systems for Terminal I/O

C-x RET t codingRET

Use coding system coding for terminal output
(set-terminal-coding-system).

C-x RET k codingRET

Use coding system coding for keyboard input
(set-keyboard-coding-system).

The command C-x RET t (set-terminal-coding-system)
specifies the coding system for terminal output. If you specify a
character code for terminal output, all characters output to the
terminal are translated into that coding system.

This feature is useful for certain character-only terminals built to
support specific languages or character sets—for example, European
terminals that support one of the ISO Latin character sets. You need to
specify the terminal coding system when using multibyte text, so that
Emacs knows which characters the terminal can actually handle.

By default, output to the terminal is not translated at all, unless
Emacs can deduce the proper coding system from your terminal type or
your locale specification (see Language Environments).

The command C-x RET k (set-keyboard-coding-system),
or the variable keyboard-coding-system, specifies the coding
system for keyboard input. Character-code translation of keyboard
input is useful for terminals with keys that send non-ASCII
graphic characters—for example, some terminals designed for ISO
Latin-1 or subsets of it.

By default, keyboard input is translated based on your system locale
setting. If your terminal does not really support the encoding
implied by your locale (for example, if you find it inserts a
non-ASCII character if you type M-i), you will need to set
keyboard-coding-system to nil to turn off encoding.
You can do this by putting

(set-keyboard-coding-system nil)

in your init file.

There is a similarity between using a coding system translation for
keyboard input, and using an input method: both define sequences of
keyboard input that translate into single characters. However, input
methods are designed to be convenient for interactive use by humans, and
the sequences that are translated are typically sequences of ASCII
printing characters. Coding systems typically translate sequences of
non-graphic characters.

22.13 Fontsets

A font typically defines shapes for a single alphabet or script.
Therefore, displaying the entire range of scripts that Emacs supports
requires a collection of many fonts. In Emacs, such a collection is
called a fontset. A fontset is defined by a list of font specifications,
each assigned to handle a range of character codes, and may fall back
on another fontset for characters that are not covered by the fonts
it specifies.

Each fontset has a name, like a font. However, while fonts are
stored in the system and the available font names are defined by the
system, fontsets are defined within Emacs itself. Once you have
defined a fontset, you can use it within Emacs by specifying its name,
anywhere that you could use a single font. Of course, Emacs fontsets
can use only the fonts that the system supports. If some characters
appear on the screen as empty boxes or hex codes, this means that the
fontset in use for them has no font for those characters. In this
case, or if the characters are shown, but not as well as you would
like, you may need to install extra fonts. Your operating system may
have optional fonts that you can install; or you can install the GNU
Intlfonts package, which includes fonts for most supported
scripts.9

Emacs creates three fontsets automatically: the standard
fontset, the startup fontset and the default fontset.
The default fontset is most likely to have fonts for a wide variety of
non-ASCII characters, and is the default fallback for the
other two fontsets, and if you set a default font rather than fontset.
However, it does not specify font family names, so results can be
somewhat random if you use it directly. You can specify use of a
particular fontset by starting Emacs with the ‘-fn’ option.
For example,

emacs -fn fontset-standard

You can also specify a fontset with the ‘Font’ resource (see X Resources).

If no fontset is specified for use, then Emacs uses an
ASCII font, with ‘fontset-default’ as a fallback for
characters the font does not cover. The standard fontset is only used if
explicitly requested, despite its name.

A fontset does not necessarily specify a font for every character
code. If a fontset specifies no font for a certain character, or if
it specifies a font that does not exist on your system, then it cannot
display that character properly. It will display that character as a
hex code or thin space or an empty box instead. (See glyphless characters, for details.)

22.14 Defining fontsets

When running on X, Emacs creates a standard fontset automatically according to the value
of standard-fontset-spec. This fontset’s name is

-*-fixed-medium-r-normal-*-16-*-*-*-*-*-fontset-standard

or just ‘fontset-standard’ for short.

On GNUstep and Mac OS X, the standard fontset is created using the value of
ns-standard-fontset-spec, and on MS Windows it is
created using the value of w32-standard-fontset-spec.

Bold, italic, and bold-italic variants of the standard fontset are
created automatically. Their names have ‘bold’ instead of
‘medium’, or ‘i’ instead of ‘r’, or both.

Emacs generates a fontset automatically, based on any default
ASCII font that you specify with the ‘Font’ resource or
the ‘-fn’ argument, or the default font that Emacs found when it
started. This is the startup fontset and its name is
fontset-startup. It does this by replacing the
charset_registry field with ‘fontset’, and replacing
charset_encoding field with ‘startup’, then using the
resulting string to specify a fontset.

For instance, if you start Emacs with a font of this form,

emacs -fn "*courier-medium-r-normal--14-140-*-iso8859-1"

Emacs generates the following fontset and uses it for the initial X
window frame:

-*-courier-medium-r-normal-*-14-140-*-*-*-*-fontset-startup

The startup fontset will use the font that you specify, or a variant
with a different registry and encoding, for all the characters that
are supported by that font, and fallback on ‘fontset-default’ for
other characters.

With the X resource ‘Emacs.Font’, you can specify a fontset name
just like an actual font name. But be careful not to specify a fontset
name in a wildcard resource like ‘Emacs*Font’—that wildcard
specification matches various other resources, such as for menus, and
menus cannot handle fontsets. See X Resources.

You can specify additional fontsets using X resources named
‘Fontset-n’, where n is an integer starting from 0.
The resource value should have this form:

fontpattern, [charset:font]…

fontpattern should have the form of a standard X font name (see
the previous fontset-startup example), except
for the last two fields. They should have the form
‘fontset-alias’.

The fontset has two names, one long and one short. The long name is
fontpattern. The short name is ‘fontset-alias’. You
can refer to the fontset by either name.

The construct ‘charset:font’ specifies which font to
use (in this fontset) for one particular character set. Here,
charset is the name of a character set, and font is the
font to use for that character set. You can use this construct any
number of times in defining one fontset.

For the other character sets, Emacs chooses a font based on
fontpattern. It replaces ‘fontset-alias’ with values
that describe the character set. For the ASCII character font,
‘fontset-alias’ is replaced with ‘ISO8859-1’.

In addition, when several consecutive fields are wildcards, Emacs
collapses them into a single wildcard. This is to prevent use of
auto-scaled fonts. Fonts made by scaling larger fonts are not usable
for editing, and scaling a smaller font is not also useful, because it is
better to use the smaller font in its own size, which is what Emacs
does.

Thus if fontpattern is this,

-*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24

the font specification for ASCII characters would be this:

-*-fixed-medium-r-normal-*-24-*-ISO8859-1

and the font specification for Chinese GB2312 characters would be this:

-*-fixed-medium-r-normal-*-24-*-gb2312*-*

You may not have any Chinese font matching the above font
specification. Most X distributions include only Chinese fonts that
have ‘song ti’ or ‘fangsong ti’ in the family field. In
such a case, ‘Fontset-n’ can be specified as:

22.15 Modifying Fontsets

Fontsets do not always have to be created from scratch. If only
minor changes are required it may be easier to modify an existing
fontset. Modifying ‘fontset-default’ will also affect other
fontsets that use it as a fallback, so can be an effective way of
fixing problems with the fonts that Emacs chooses for a particular
script.

Fontsets can be modified using the function set-fontset-font,
specifying a character, a charset, a script, or a range of characters
to modify the font for, and a font specification for the font to be
used. Some examples are:

22.16 Undisplayable Characters

There may be some non-ASCII characters that your
terminal cannot display. Most text terminals support just a single
character set (use the variable default-terminal-coding-system
to tell Emacs which one, Terminal Coding); characters that
can’t be encoded in that coding system are displayed as ‘?’ by
default.

Graphical displays can display a broader range of characters, but
you may not have fonts installed for all of them; characters that have
no font appear as a hollow box.

If you use Latin-1 characters but your terminal can’t display
Latin-1, you can arrange to display mnemonic ASCII sequences
instead, e.g., ‘"o’ for o-umlaut. Load the library
iso-ascii to do this.

If your terminal can display Latin-1, you can display characters
from other European character sets using a mixture of equivalent
Latin-1 characters and ASCII mnemonics. Customize the variable
latin1-display to enable this. The mnemonic ASCII
sequences mostly correspond to those of the prefix input methods.

22.17 Unibyte Editing Mode

The ISO 8859 Latin-n character sets define character codes in
the range 0240 to 0377 octal (160 to 255 decimal) to handle the
accented letters and punctuation needed by various European languages
(and some non-European ones). Note that Emacs considers bytes with
codes in this range as raw bytes, not as characters, even in a unibyte
buffer, i.e., if you disable multibyte characters. However, Emacs can
still handle these character codes as if they belonged to one
of the single-byte character sets at a time. To specify which
of these codes to use, invoke M-x set-language-environment and
specify a suitable language environment such as ‘Latin-n’.
See Disabling Multibyte Characters in GNU Emacs Lisp Reference Manual.

Emacs can also display bytes in the range 160 to 255 as readable
characters, provided the terminal or font in use supports them. This
works automatically. On a graphical display, Emacs can also display
single-byte characters through fontsets, in effect by displaying the
equivalent multibyte characters according to the current language
environment. To request this, set the variable
unibyte-display-via-language-environment to a non-nil
value. Note that setting this only affects how these bytes are
displayed, but does not change the fundamental fact that Emacs treats
them as raw bytes, not as characters.

If your terminal does not support display of the Latin-1 character
set, Emacs can display these characters as ASCII sequences which at
least give you a clear idea of what the characters are. To do this,
load the library iso-ascii. Similar libraries for other
Latin-n character sets could be implemented, but have not been
so far.

Normally non-ISO-8859 characters (decimal codes between 128 and 159
inclusive) are displayed as octal escapes. You can change this for
non-standard “extended” versions of ISO-8859 character sets by using the
function standard-display-8bit in the disp-table library.

There are two ways to input single-byte non-ASCII
characters:

You can use an input method for the selected language environment.
See Input Methods. When you use an input method in a unibyte buffer,
the non-ASCII character you specify with it is converted to unibyte.

If your keyboard can generate character codes 128 (decimal) and up,
representing non-ASCII characters, you can type those character codes
directly.

On a graphical display, you should not need to do anything special to
use these keys; they should simply work. On a text terminal, you
should use the command M-x set-keyboard-coding-system or customize the
variable keyboard-coding-system to specify which coding system
your keyboard uses (see Terminal Coding). Enabling this feature
will probably require you to use ESC to type Meta characters;
however, on a console terminal or in xterm, you can arrange for
Meta to be converted to ESC and still be able type 8-bit
characters present directly on the keyboard or using Compose or
AltGr keys. See User Input.

For Latin-1 only, you can use the key C-x 8 as a “compose
character” prefix for entry of non-ASCII Latin-1 printing
characters. C-x 8 is good for insertion (in the minibuffer as
well as other buffers), for searching, and in any other context where
a key sequence is allowed.

C-x 8 works by loading the iso-transl library. Once that
library is loaded, the Alt modifier key, if the keyboard has
one, serves the same purpose as C-x 8: use Alt together
with an accent character to modify the following letter. In addition,
if the keyboard has keys for the Latin-1 “dead accent characters”,
they too are defined to compose with the following character, once
iso-transl is loaded.

22.18 Charsets

In Emacs, charset is short for “character set”. Emacs
supports most popular charsets (such as ascii,
iso-8859-1, cp1250, big5, and unicode), in
addition to some charsets of its own (such as emacs,
unicode-bmp, and eight-bit). All supported characters
belong to one or more charsets.

Emacs normally “does the right thing” with respect to charsets, so
that you don’t have to worry about them. However, it is sometimes
helpful to know some of the underlying details about charsets.

One example is font selection (see Fonts). Each language
environment (see Language Environments) defines a “priority
list” for the various charsets. When searching for a font, Emacs
initially attempts to find one that can display the highest-priority
charsets. For instance, in the Japanese language environment, the
charset japanese-jisx0208 has the highest priority, so Emacs
tries to use a font whose registry property is
‘JISX0208.1983-0’.

There are two commands that can be used to obtain information about
charsets. The command M-x list-charset-chars prompts for a
charset name, and displays all the characters in that character set.
The command M-x describe-character-set prompts for a charset
name, and displays information about that charset, including its
internal representation within Emacs.

M-x list-character-sets displays a list of all supported
charsets. The list gives the names of charsets and additional
information to identity each charset; see the
International Register of
Coded Character Sets for more details. In this list,
charsets are divided into two categories: normal charsets are
listed first, followed by supplementary charsets. A
supplementary charset is one that is used to define another charset
(as a parent or a subset), or to provide backward-compatibility for
older Emacs versions.

To find out which charset a character in the buffer belongs to, put
point before it and type C-u C-x = (see International Chars).

22.19 Bidirectional Editing

Emacs supports editing text written in scripts, such as Arabic and
Hebrew, whose natural ordering of horizontal text for display is from
right to left. However, digits and Latin text embedded in these
scripts are still displayed left to right. It is also not uncommon to
have small portions of text in Arabic or Hebrew embedded in an otherwise
Latin document; e.g., as comments and strings in a program source
file. For these reasons, text that uses these scripts is actually
bidirectional: a mixture of runs of left-to-right and
right-to-left characters.

This section describes the facilities and options provided by Emacs
for editing bidirectional text.

Emacs stores right-to-left and bidirectional text in the so-called
logical (or reading) order: the buffer or string position
of the first character you read precedes that of the next character.
Reordering of bidirectional text into the visual order happens
at display time. As result, character positions no longer increase
monotonically with their positions on display. Emacs implements the
Unicode Bidirectional Algorithm described in the Unicode Standard
Annex #9, for reordering of bidirectional text for display.

The buffer-local variable bidi-display-reordering controls
whether text in the buffer is reordered for display. If its value is
non-nil, Emacs reorders characters that have right-to-left
directionality when they are displayed. The default value is
t.

Each paragraph of bidirectional text can have its own base
direction, either right-to-left or left-to-right. (Paragraph
boundaries are empty lines, i.e., lines consisting entirely of
whitespace characters.) Text in left-to-right paragraphs begins on
the screen at the left margin of the window and is truncated or
continued when it reaches the right margin. By contrast, text in
right-to-left paragraphs is displayed starting at the right margin and
is continued or truncated at the left margin.

Emacs determines the base direction of each paragraph dynamically,
based on the text at the beginning of the paragraph. However,
sometimes a buffer may need to force a certain base direction for its
paragraphs. The variable bidi-paragraph-direction, if
non-nil, disables the dynamic determination of the base
direction, and instead forces all paragraphs in the buffer to have the
direction specified by its buffer-local value. The value can be either
right-to-left or left-to-right. Any other value is
interpreted as nil.

Alternatively, you can control the base direction of a paragraph by
inserting special formatting characters in front of the paragraph.
The special character RIGHT-TO-LEFT MARK, or RLM, forces
the right-to-left direction on the following paragraph, while
LEFT-TO-RIGHT MARK, or LRM forces the left-to-right
direction. (You can use C-x 8 RET to insert these characters.)
In a GUI session, the LRM and RLM characters display as very
thin blank characters; on text terminals they display as blanks.

Because characters are reordered for display, Emacs commands that
operate in the logical order or on stretches of buffer positions may
produce unusual effects. For example, C-f and C-b
commands move point in the logical order, so the cursor will sometimes
jump when point traverses reordered bidirectional text. Similarly, a
highlighted region covering a contiguous range of character positions
may look discontinuous if the region spans reordered text. This is
normal and similar to the behavior of other programs that support
bidirectional text. If you set visual-order-cursor-movement to
a non-nil value, cursor motion by the arrow keys follows the
visual order on screen (see visual-order movement).

23 Major and Minor Modes

Emacs contains many editing modes that alter its basic
behavior in useful ways. These are divided into major modes and
minor modes.

Major modes provide specialized facilities for working on a
particular file type, such as a C source file (see Programs), or a
particular type of non-file buffer, such as a shell buffer
(see Shell). Major modes are mutually exclusive; each buffer has
one and only one major mode at any time.

Minor modes are optional features which you can turn on or off, not
necessarily specific to a type of file or buffer. For example, Auto
Fill mode is a minor mode in which SPC breaks lines between
words as you type (see Auto Fill). Minor modes are independent of
one another, and of the selected major mode.

23.1 Major Modes

Every buffer possesses a major mode, which determines the editing
behavior of Emacs while that buffer is current. The mode line
normally shows the name of the current major mode, in parentheses
(see Mode Line).

The least specialized major mode is called Fundamental mode.
This mode has no mode-specific redefinitions or variable settings, so
that each Emacs command behaves in its most general manner, and each
user option variable is in its default state.

For editing text of a specific type that Emacs knows about, such as
Lisp code or English text, you typically use a more specialized major
mode, such as Lisp mode or Text mode. Most major modes fall into
three major groups. The first group contains modes for normal text,
either plain or with mark-up. It includes Text mode, HTML mode, SGML
mode, TeX mode and Outline mode. The second group contains modes
for specific programming languages. These include Lisp mode (which
has several variants), C mode, Fortran mode, and others. The third
group consists of major modes that are not associated directly with
files; they are used in buffers created for specific purposes by
Emacs, such as Dired mode for buffers made by Dired (see Dired),
Message mode for buffers made by C-x m (see Sending Mail),
and Shell mode for buffers used to communicate with an inferior shell
process (see Interactive Shell).

Usually, the major mode is automatically set by Emacs, when you
first visit a file or create a buffer (see Choosing Modes). You
can explicitly select a new major mode by using an M-x command.
Take the name of the mode and add -mode to get the name of the
command to select that mode (e.g., M-x lisp-mode enters Lisp mode).

The value of the buffer-local variable major-mode is a symbol
with the same name as the major mode command (e.g., lisp-mode).
This variable is set automatically; you should not change it yourself.

The default value of major-mode determines the major mode to
use for files that do not specify a major mode, and for new buffers
created with C-x b. Normally, this default value is the symbol
fundamental-mode, which specifies Fundamental mode. You can
change this default value via the Customization interface (see Easy Customization), or by adding a line like this to your init file
(see Init File):

(setq-default major-mode 'text-mode)

If the default value of major-mode is nil, the major
mode is taken from the previously current buffer.

Specialized major modes often change the meanings of certain keys to
do something more suitable for the mode. For instance, programming
language modes bind TAB to indent the current line according to
the rules of the language (see